making the underlayer min-height instead of height, to see the wrap guide go full screen

src/app/editor.coffee

@@ -746,7 +746,7 @@ class Editor extends View
     height = @lineHeight * @screenLineCount()
     unless @layerHeight == height
       @renderedLines.height(height)
-      @underlayer.height(height)
+      @underlayer.css('min-height', height)
       @overlayer.height(height)
       @layerHeight = height