Fix the pushSHA test

Author: tiennou

ObjectiveGitTests/GTEnumeratorSpec.m

@@ -31,10 +31,12 @@
 	GTReference *HEADRef = [repo headReferenceWithError:NULL];
 	expect(HEADRef).notTo(beNil());
 
-	[enumerator pushSHA:HEADRef.targetOID.SHA error:NULL];
+	BOOL success = [enumerator pushSHA:HEADRef.targetOID.SHA error:&error];
+	expect(@(success)).to(beTruthy());
+	expect(error).to(beNil());
+
 	NSUInteger count = [enumerator allObjects].count;
 	expect(@(count)).to(equal(@3));
-	expect(error).to(beNil());
 });
 
 describe(@"with a rev list", ^{