Render the line numbers after gutter mount

Fixes #2916

src/gutter-component.coffee

@@ -41,6 +41,7 @@ GutterComponent = React.createClass
 
   componentDidMount: ->
     @appendDummyLineNumber()
+    @updateLineNumbers() if @props.renderedRowRange?
 
   # Only update the gutter if the visible row range has changed or if a
   # non-zero-delta change to the screen lines has occurred within the current