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

PS.: I just tried it with my Fragments using the HoloEverywhere library