Fix error thrown when there's nothing to push

src/git/git.go

 		return err
 	}
 
-	return r.Push(&git.PushOptions{
+	err = r.Push(&git.PushOptions{
 		Auth: auth,
 	})
+
+	if err == git.NoErrAlreadyUpToDate {
+		return nil
+	}
+
+	return err
 }