Fix a reference to OBJ_* in the README.
Fix a reference to OBJ_* in the README.

tpickett66/rugged,Acidburn0zzz/rugged,libgit2/rugged,tpickett66/rugged,spraints/rugged,Acidburn0zzz/rugged,spraints/rugged,libgit2/rugged,Acidburn0zzz/rugged,saraid/rugged,saraid/rugged,libgit2/rugged,saraid/rugged,tpickett66/rugged