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

Committed via https://github.com/asottile/all-repos
diff --git a/pre_commit_hooks/trailing_whitespace_fixer.py b/pre_commit_hooks/trailing_whitespace_fixer.py
index 05ed999..82faa2d 100644
--- a/pre_commit_hooks/trailing_whitespace_fixer.py
+++ b/pre_commit_hooks/trailing_whitespace_fixer.py
@@ -99,4 +99,4 @@
 
 
 if __name__ == '__main__':
-    exit(main())
+    raise SystemExit(main())