Try to fix the 1.8.7 and 2.0.0 build failures.
Try to fix the 1.8.7 and 2.0.0 build failures.

1.8.7: https://travis-ci.org/libgit2/rugged/jobs/7235525#L92
2.0.0: https://travis-ci.org/libgit2/rugged/jobs/7235527#L92

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