docs: replace the codeql badge (#290)

Signed-off-by: Keming <kemingy94@gmail.com>

README.md

@@ -4,7 +4,7 @@
 [![GitHub Actions](https://github.com/0b01001001/spectree/workflows/Python%20package/badge.svg)](https://github.com/0b01001001/spectree/actions)
 [![pypi](https://img.shields.io/pypi/v/spectree.svg)](https://pypi.python.org/pypi/spectree)
 [![versions](https://img.shields.io/pypi/pyversions/spectree.svg)](https://github.com/0b01001001/spectree)
-[![Language grade: Python](https://img.shields.io/lgtm/grade/python/g/0b01001001/spectree.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/0b01001001/spectree/context:python)
+[![CodeQL](https://github.com/0b01001001/spectree/actions/workflows/codeql.yml/badge.svg)](https://github.com/0b01001001/spectree/actions/workflows/codeql.yml)
 [![Python document](https://github.com/0b01001001/spectree/workflows/Python%20document/badge.svg)](https://0b01001001.github.io/spectree/)
 
 Yet another library to generate OpenAPI documents and validate requests & responses with Python annotations.