Migrate to font-awesome 5.0. (#8799)

app/javascript/mastodon/components/__tests__/__snapshots__/avatar-test.js.snap

@@ -15,7 +15,7 @@ exports[`<Avatar /> Autoplay renders a animated avatar 1`] = `
   }
 >
   <i
-    className="fa fa-fw fa-robot bot-icon"
+    className="fas fa-fw fa-robot bot-icon"
   />
 </div>
 `;
@@ -35,7 +35,7 @@ exports[`<Avatar /> Still renders a still avatar 1`] = `
   }
 >
   <i
-    className="fa fa-fw fa-robot bot-icon"
+    className="fas fa-fw fa-robot bot-icon"
   />
 </div>
 `;