the c(h)at's name

Add some keys translation to named the rocketchat tab to happychat project (happydev Paris).

src/locales/en.json

@@ -33,7 +33,8 @@
     "circlesBrowse": "Browse circles",
     "circleCreate": "Create circle",
     "messages": "Messages",
-    "search": "Search (ctrl+k)"
+    "search": "Search (ctrl+k)",
+    "rocketchat": "Chat"
   },
   "about": {
     "title": "About",