Fix readCommonAncestor to keep lineage of ancestors
Fix readCommonAncestor to keep lineage of ancestors

* Was stupidly sorting after getting common ancestors, which meant that the a non-most-recent ancestor was getting returned in some cases.  The sorting was there to make rCA results commutative.  Solved the problem by sorting the input hashes, instead.
pirafrank/gitlet,pirafrank/gitlet,harrytruong/gitlet,maryrosecook/gitlet,pysnow530/gitlet,maryrosecook/gitlet,harrytruong/gitlet