Fixing actually broken code found by es6

revWalk.repo only has a getter and you don't need to set it because it's already handled at the libgit2 level.

Author: cbargren

lib/repository.js

@@ -428,9 +428,7 @@ Repository.prototype.deleteTagByName = function(name) {
  * @return {RevWalk}
  */
 Repository.prototype.createRevWalk = function() {
-  var revWalk = Revwalk.create(this);
-  revWalk.repo = this;
-  return revWalk;
+  return Revwalk.create(this);
 };
 
 /**