Add proguard rule so that ripple effect can work in release package

[markzhai]

As nineoldandroids ObjectAnimator uses reflection to access get/sets, we
need proguard rules to protect RippleDrawable.

[saket]

Thank you!

[ypresto]

Package name is changed, use below snippet for 2.0.0+.

-keep class codetail.graphics.drawables.** { *; }