grid lines showing inside the bar graph

What steps will reproduce the problem?
1.enable grid lines
2. show bar chart
3.

What is the expected output? What do you see instead?
When gridlines are enabled, the lines overlap within the bar graph as well. I 
want the grid lines only outside the bar graph

Please provide a source code snippet that we can use to replicate the
issue.

What version of the product binary library are you using?
I have forked the source code and modified it for customizing. The latest 
version also doesn't have that feature i.e. 1.0.1

Please provide any additional information below.

Original issue reported on code.google.com by nizeshsh...@gmail.com on 11 Jul 2014 at 10:20

wangyao5 / achartengine

grid lines showing inside the bar graph #419