Update LineGraph.java

Multiply sidePadding for usableWidth with 2 (left+right) 

-> Otherwise a Point at the max value on X-axis is out of Fragment:

Issue:
http://www.abload.de/image.php?img=holographlibrary_linekdk1h.png

Fix:
http://abload.de/img/holographlibrary_linef7kq4.png
Merge pull request #9 from steinhoff1989/patch-1

Update LineGraph.java