Use os.path.relpath

Author: schedutron

script/validators/source_validator.py

@@ -259,7 +259,7 @@ def validate_file(file_path):
         if not validator(file_path):
             file_status = False
 
-    relative_path = file_path.replace(PELOTON_DIR, '')
+    relative_path = os.path.relpath(file_path, start=PELOTON_DIR)
     if relative_path.startswith('/test/') and relative_path.endswith('.cpp'):
         if not relative_path.endswith('_util.cpp'):
             file_status = check_tests(file_path)