Fix "Plus" icon size in dashboard (part 2)

public/ng/less/gogs/dashboard.less

@@ -159,7 +159,7 @@
   padding-top: 6px;
   margin-right: 1px;
   .octicon {
-    font-size: 2em;
+    font-size: 20px;
   }
   border-top-left-radius: .3em;
   border-top-right-radius: .3em;