🐛 Make sure grep uses extended regex syntax

Otherwise it will complain about the escaped brackets. We do WANT to
escape them though since we want to use the same pattern also in our
fallback implementation in case grep isn't available.

Closes #2

Author: foosel

octoprint_file_check/__init__.py

@@ -84,7 +84,7 @@ def _search_through_file(self, path, term, incl_comments=False):
 
         try:
             # try native grep
-            result = sarge.run(["grep", "-q", pattern, path])
+            result = sarge.run(["grep", "-q", "-E", pattern, path])
             return result.returncode == 0
         except ValueError as exc:
             if "Command not found" in str(exc):