Fix wrong call to HasPrefix

src/git/git.go

 
 	// go-git doesn't have an error variable for "non-fast-forward update", so
 	// this is the only way to detect it
-	if strings.HasPrefix("non-fast-forward update", err.Error()) {
+	if strings.HasPrefix(err.Error(), "non-fast-forward update") {
 		return r, nil
 	}
 
 
 	// go-git doesn't have an error variable for "non-fast-forward update", so
 	// this is the only way to detect it
-	if strings.HasPrefix("non-fast-forward update", err.Error()) {
+	if strings.HasPrefix(err.Error(), "non-fast-forward update") {
 		return nil
 	}