replace exit(main()) with raise SystemExit(main())

Committed via https://github.com/asottile/all-repos
diff --git a/pre_commit_hooks/check_merge_conflict.py b/pre_commit_hooks/check_merge_conflict.py
index dc25b29..aed1e9c 100644
--- a/pre_commit_hooks/check_merge_conflict.py
+++ b/pre_commit_hooks/check_merge_conflict.py
@@ -51,4 +51,4 @@
 
 
 if __name__ == '__main__':
-    exit(main())
+    raise SystemExit(main())