pinned version of flask, to match cellxgene

.pre-commit-config.yaml

@@ -8,7 +8,6 @@ repos:
       types: [python]
       stages: [commit]
     - id: black
-      language_version: python3.6+
       name: black
       language: system
       entry: black

environment.yml

@@ -4,7 +4,7 @@ channels:
 dependencies:
 - python=3.7
 - requests
-- flask
+- flask<2.0.0,>=1.0.2
 - psutil
 - black
 - coverage

requirements.txt

@@ -1,5 +1,5 @@
 cellxgene>=0.15
-flask
+flask<2.0.0,>=1.0.2
 flask_api
 psutil
 requests