Add slack icon

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
   - `cloud-snow`
   - `codepen`
   - `repeat`
+  - `slack`
 </details>
 
 ### Changed

icons/logos/slack.svg

+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24">
+    <path d="M22.08 9C19.81 1.41 16.54-.35 9 1.92S-.35 7.46 1.92 15 7.46 24.35 15 22.08 24.35 16.54 22.08 9z" fill="none" stroke="#000" stroke-miterlimit="10" stroke-width="2"/>
+    <line x1="12.57" y1="5.99" x2="16.15" y2="16.39" fill="none" stroke="#000" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2"/>
+    <line x1="7.85" y1="7.61" x2="11.43" y2="18.01" fill="none" stroke="#000" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2"/>
+    <line x1="16.39" y1="7.85" x2="5.99" y2="11.43" fill="none" stroke="#000" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2"/>
+    <line x1="18.01" y1="12.57" x2="7.61" y2="16.15" fill="none" stroke="#000" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2"/>
+</svg>