Update dependency flask-session to v0.4.0

Author: renovate-bot

requirements.txt

@@ -7,7 +7,7 @@ dnspython==2.0.0; python_version >= "3.6"
 email-validator==1.1.1
 flask-assets==2.0
 flask-login==0.5.0
-flask-session==0.3.2
+flask-session==0.4.0
 flask-sqlalchemy==2.4.4; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.4.0")
 flask-wtf==0.15.1
 flask==1.1.2; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.5.0")