Explicitly specify algorithm for JAR signing.
Explicitly specify algorithm for JAR signing.

This fixes compatibility with Android 4.3 and lower. The Enabler is
built using JDK 7, which changed the default signing algorithm. It no
longer matches what is used in these older versions of Android.

Fixed #210.

openxc/openxc-android,prateeknitish391/demo,dhootha/openxc-android,prateeknitish391/demo,petemaclellan/openxc-android,mray19027/openxc-android,ChernyshovYuriy/openxc-android,msowka/openxc-android,petemaclellan/openxc-android,msowka/openxc-android,openxc/openxc-android,mray19027/openxc-android,prateeknitish391/demo,dhootha/openxc-android,ChernyshovYuriy/openxc-android