Add flask to test reqs (needed for moto server)

Martin Durant · Martin Durant · commit 7ad67e16e711 · 2020-09-11T10:08:11.000-04:00
diff --git a/requirements_dev_optional.txt b/requirements_dev_optional.txt
@@ -20,3 +20,4 @@ pytest-remotedata==0.3.2
 h5py==2.10.0
 s3fs==0.5.0; python_version > '3.6'
 moto>=1.3.14; python_version > '3.6'
+flask
