Use spacepen for html generation

For consistency

src/root-view.coffee

@@ -65,7 +65,7 @@ class RootView extends View
 
   # Private:
   initialize: (state={}) ->
-    @prepend("<div class='dev-mode'></div>") if atom.getLoadSettings().devMode
+    @prepend($$ -> @div class: 'dev-mode') if atom.getLoadSettings().devMode
 
     if state instanceof telepath.Document
       @state = state