Add Pipfile.lock to list of excluded lockfiles

Updates is_lock_file to include Pipfile.lock when checking for lock files to exclude.

detect_secrets/filters/heuristic.py

@@ -194,6 +194,7 @@ def is_lock_file(filename: str) -> bool:
         'package-lock.json',
         'Podfile.lock',
         'yarn.lock',
+        'Pipfile.lock',
     }