Give React editor lines and line numbers an opaque background

This ensures subpixel antialiasing works correctly. It was previously
present on both of these components but got dropped accidentally.

src/gutter-component.coffee

@@ -17,7 +17,7 @@ GutterComponent = React.createClass
     {scrollHeight, scrollTop} = @props
 
     div className: 'gutter', onClick: @onClick,
-      div className: 'line-numbers', ref: 'lineNumbers', style:
+      div className: 'line-numbers editor-colors', ref: 'lineNumbers', style:
         height: scrollHeight
         WebkitTransform: "translate3d(0px, #{-scrollTop}px, 0px)"
 

src/lines-component.coffee

@@ -21,7 +21,7 @@ LinesComponent = React.createClass
         width: scrollWidth
         WebkitTransform: "translate3d(#{-scrollLeft}px, #{-scrollTop}px, 0px)"
 
-    div {className: 'lines', style},
+    div {className: 'lines editor-colors', style},
       SelectionsComponent({editor, selectionScreenRanges, lineHeightInPixels, defaultCharWidth}) if @isMounted()
 
   componentWillMount: ->