beta1 blog entry: Fix CoffeeScript example

Fix the constructor call and make code more idiomatic.

docs/_posts/2015-01-27-react-v0.13.0-beta-1.md

@@ -135,17 +135,20 @@ You can also use CoffeeScript classes:
 div = React.createFactory 'div'
 
 class Counter extends React.Component
-  @propTypes =
-    initialCount: React.PropTypes.number
-  @defaultProps =
-    initialCount: 0
-  constructor: ->
-    @state =
-      count: @props.initialCount
+  @propTypes = initialCount: React.PropTypes.number
+  @defaultProps = initialCount: 0
+
+  constructor: (props) ->
+    super props
+    @state = count: props.initialCount
+
   tick: =>
     @setState count: @state.count + 1
+
   render: ->
-    div(onClick: @tick, 'Clicks: ', @state.count)
+    div onClick: @tick,
+      'Clicks: '
+      @state.count
 ```
 
 You can even use the old ES3 module pattern if you want: