fix:dismiss soft keyboard on pressing submit button in server url fragment

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

@@ -6,6 +6,7 @@ import android.support.annotation.Nullable;
 import android.support.constraint.ConstraintLayout;
 import android.support.design.widget.Snackbar;
 import android.view.View;
+import android.view.inputmethod.InputMethodManager;
 import android.widget.TextView;
 
 import chat.rocket.android.BuildConfig;
@@ -25,7 +26,8 @@ public class InputHostnameFragment extends AbstractFragment implements InputHost
     private ConstraintLayout container;
     private View waitingView;
 
-  public InputHostnameFragment() {}
+    public InputHostnameFragment() {
+    }
 
     @Override
     public void onCreate(@Nullable Bundle savedInstanceState) {
@@ -55,9 +57,17 @@ public class InputHostnameFragment extends AbstractFragment implements InputHost
     }
 
     private void handleConnect() {
+        hideSoftKeyboard();
         presenter.connectTo(getHostname());
     }
 
+    private void hideSoftKeyboard() {
+        InputMethodManager inputManager = (InputMethodManager)
+                getActivity().getSystemService(Context.INPUT_METHOD_SERVICE);
+        inputManager.hideSoftInputFromWindow(getActivity().getCurrentFocus().getWindowToken(),
+                InputMethodManager.HIDE_NOT_ALWAYS);
+    }
+
     @Override
     public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
         super.onViewCreated(view, savedInstanceState);