Updated build.gradle, fixed scrollToEnd and can now set bottom margin of legend

I had a problem with scrollToEnd after the following commit: https://github.com/jjoe64/GraphView/commit/ba7ed0f40925a3523f7a74eb5dac8eae1f5cb72a#diff-132b92aa11d9833e422aefc0febf1558R615, as it would set textHeight and textWidth to null every time scrollToEnd was called. This meant that the border of the graph flickered up and down, as it would recalculate the height and width every time onDraw was called.


The screenshots below shows the behaviour of setLegendMarginBottom:

No margin (default):
![2013-12-01 16 29 30](https://f.cloud.github.com/assets/1098847/1650710/36856886-5aa7-11e3-89ec-1408d9d333b4.png)

Margin of 30:
![2013-12-01 16 30 20](https://f.cloud.github.com/assets/1098847/1650709/3662fa58-5aa7-11e3-8c03-72b25837220f.png)