Update README.md

remove non functional lgtm badge

Author: vegu

README.md

@@ -4,7 +4,6 @@
 [![PyPI](https://img.shields.io/pypi/v/django-handleref.svg?maxAge=3600)](https://pypi.python.org/pypi/django-handleref)
 [![PyPI](https://img.shields.io/pypi/pyversions/django-handleref.svg?maxAge=600)](https://pypi.python.org/pypi/django-handleref)
 [![Tests](https://github.com/20c/django-handleref/workflows/tests/badge.svg)](https://github.com/20c/django-handleref)
-[![LGTM Grade](https://img.shields.io/lgtm/grade/python/github/20c/django-handleref)](https://lgtm.com/projects/g/20c/django-handleref/alerts/)
 [![Codecov](https://img.shields.io/codecov/c/github/20c/django-handleref/master.svg?maxAge=3600)](https://codecov.io/github/20c/django-handleref)
 
 track when an object was created or changed and allow querying based on time and versioning (w/ django-reversion support)