AK2+Backend: fix file_getprop truncating if prop value contained =

See comments: https://github.com/osm0sis/AnyKernel2/pull/35#issuecomment-447648900

META-INF/com/google/android/update-binary

@@ -13,7 +13,7 @@ ui_print() {
   done;
 }
 show_progress() { echo "progress $1 $2" > $OUTFD; }
-file_getprop() { $bb grep "^$2=" "$1" | $bb cut -d= -f2; }
+file_getprop() { $bb grep "^$2=" "$1" | $bb cut -d= -f2-; }
 cleanup() {
   cd /tmp;
   rm -rf /tmp/anykernel;