Update classes.

app/src/main/java/chat/rocket/android/RocketChatApplication.java

 package chat.rocket.android;
 
 import android.support.multidex.MultiDexApplication;
+import chat.rocket.android.helper.OkHttpHelper;
 import com.crashlytics.android.Crashlytics;
 
 import io.fabric.sdk.android.Fabric;
 import java.util.List;
-import chat.rocket.android.helper.OkHttpHelper;
 import chat.rocket.persistence.realm.RealmStore;
 import chat.rocket.android.service.ConnectivityManager;
 import chat.rocket.core.models.ServerInfo;
@@ -29,6 +29,6 @@ public class RocketChatApplication extends MultiDexApplication {
       RealmStore.put(serverInfo.getHostname());
     }
 
-    RocketChatWidgets.initialize(this, OkHttpHelper.getClientForDownloadFile(this));
+    RocketChatWidgets.initialize(this, OkHttpHelper.INSTANCE.getClientForDownloadFile(this));
   }
 }
\ No newline at end of file

app/src/main/java/chat/rocket/android/api/DDPClientWrapper.java

@@ -2,13 +2,13 @@ package chat.rocket.android.api;
 
 import android.support.annotation.Nullable;
 
+import chat.rocket.android.helper.OkHttpHelper;
 import org.json.JSONArray;
 import org.json.JSONException;
 
 import java.util.UUID;
 
 import bolts.Task;
-import chat.rocket.android.helper.OkHttpHelper;
 import chat.rocket.android.helper.TextUtils;
 import chat.rocket.android.log.RCLog;
 import chat.rocket.android_ddp.DDPClient;
@@ -25,7 +25,7 @@ public class DDPClientWrapper {
   private final String hostname;
 
   private DDPClientWrapper(String hostname) {
-    ddpClient = new DDPClient(OkHttpHelper.getClientForWebSocket());
+    ddpClient = new DDPClient(OkHttpHelper.INSTANCE.getClientForWebSocket());
     this.hostname = hostname;
   }
 

app/src/main/java/chat/rocket/android/fragment/add_server/InputHostnamePresenter.java

 package chat.rocket.android.fragment.add_server;
 
 import chat.rocket.android.BackgroundLooper;
+import chat.rocket.android.helper.OkHttpHelper;
 import io.reactivex.android.schedulers.AndroidSchedulers;
 import io.reactivex.disposables.Disposable;
 
 import chat.rocket.android.RocketChatCache;
 import chat.rocket.android.api.rest.DefaultServerPolicyApi;
 import chat.rocket.android.api.rest.ServerPolicyApi;
-import chat.rocket.android.helper.OkHttpHelper;
 import chat.rocket.android.helper.ServerPolicyApiValidationHelper;
 import chat.rocket.android.helper.ServerPolicyHelper;
 import chat.rocket.android.service.ConnectivityManagerApi;
@@ -29,7 +29,7 @@ public class InputHostnamePresenter extends BasePresenter<InputHostnameContract.
   }
 
   public void connectToEnforced(final String hostname) {
-    final ServerPolicyApi serverPolicyApi = new DefaultServerPolicyApi(OkHttpHelper.getClientForUploadFile(), hostname);
+    final ServerPolicyApi serverPolicyApi = new DefaultServerPolicyApi(OkHttpHelper.INSTANCE.getClientForUploadFile(), hostname);
     final ServerPolicyApiValidationHelper validationHelper = new ServerPolicyApiValidationHelper(serverPolicyApi);
 
     clearSubscriptions();

app/src/main/java/chat/rocket/android/service/observer/FileUploadingToUrlObserver.java

@@ -2,6 +2,7 @@ package chat.rocket.android.service.observer;
 
 import android.content.Context;
 import android.net.Uri;
+import chat.rocket.android.helper.OkHttpHelper;
 import io.realm.Realm;
 import io.realm.RealmResults;
 import org.json.JSONArray;
@@ -13,7 +14,6 @@ import java.util.List;
 import bolts.Task;
 import chat.rocket.android.api.FileUploadingHelper;
 import chat.rocket.android.helper.LogIfError;
-import chat.rocket.android.helper.OkHttpHelper;
 import chat.rocket.android.log.RCLog;
 import chat.rocket.core.SyncState;
 import chat.rocket.persistence.realm.models.internal.FileUploading;
@@ -167,7 +167,7 @@ public class FileUploadingToUrlObserver extends AbstractModelObserver<FileUpload
           .post(bodyBuilder.build())
           .build();
 
-      Response response = OkHttpHelper.getClientForUploadFile().newCall(request).execute();
+      Response response = OkHttpHelper.INSTANCE.getClientForUploadFile().newCall(request).execute();
       if (response.isSuccessful()) {
         return Task.forResult(downloadUrl);
       } else {

app/src/main/java/chat/rocket/android/service/observer/FileUploadingWithUfsObserver.java

@@ -2,6 +2,7 @@ package chat.rocket.android.service.observer;
 
 import android.content.Context;
 import android.net.Uri;
+import chat.rocket.android.helper.OkHttpHelper;
 import io.realm.Realm;
 import io.realm.RealmResults;
 import org.json.JSONObject;
@@ -11,7 +12,6 @@ import java.util.List;
 import bolts.Task;
 import chat.rocket.android.api.FileUploadingHelper;
 import chat.rocket.android.helper.LogIfError;
-import chat.rocket.android.helper.OkHttpHelper;
 import chat.rocket.android.log.RCLog;
 import chat.rocket.core.SyncState;
 import chat.rocket.persistence.realm.models.ddp.RealmUser;
@@ -143,7 +143,7 @@ public class FileUploadingWithUfsObserver extends AbstractModelObserver<FileUplo
               .post(RequestBody.create(contentType, buffer, 0, read))
               .build();
 
-          Response response = OkHttpHelper.getClientForUploadFile().newCall(request).execute();
+          Response response = OkHttpHelper.INSTANCE.getClientForUploadFile().newCall(request).execute();
           if (response.isSuccessful()) {
             final JSONObject obj = new JSONObject()
                 .put(FileUploading.ID, uplId)