[AIRFLOW-4905] Add colours to flake8 output (#5541)

.flake8

@@ -2,3 +2,4 @@
 max-line-length = 110
 ignore = E731,W504
 exclude = .svn,CVS,.bzr,.hg,.git,__pycache__,.tox,.eggs,*.egg,*/_vendor/*,node_modules
+format = ${cyan}%(path)s${reset}:${yellow_bold}%(row)d${reset}:${green_bold}%(col)d${reset}: ${red_bold}%(code)s${reset} %(text)s

setup.py

@@ -280,6 +280,7 @@ devel = [
     'beautifulsoup4~=4.7.1',
     'click==6.7',
     'flake8>=3.6.0',
+    'flake8-colors',
     'freezegun',
     'jira',
     'mongomock',