[DO NOT MERGE] -keepclasses is not a proguard option

It looks like proguard is accepting it and make completion to a valid
option even if there's ambiguity beetwen -keepclasseswithmembers and
-keepclasseswithmembernames. Jack is not permitting that kind of
incomplete options, so fixing.

(cherry picked from commit c407643689445e23a5b4ed6cd1a81065b825cfa5)

Change-Id: Id8f5d5a8a74398183d234ce9cbe985552bc7d63c
1 file changed