Automatically install mypy stubs

New mypy version 0.911 adds a --non-interactive option allowing us to
install mypy stubs automatically and non interactively with
--install-types --non-interactive.

Reviewed By: PrzemekWirkus

Differential Revision: https://reviews.llvm.org/D104775

Author: Thomas Preud'homme

tox.ini

@@ -17,18 +17,12 @@ commands =
 basepython = python3
 skip_install = true
 deps =
-    mypy
+    mypy >= 0.910
     sqlalchemy-stubs
-    types-Flask
-    types-Jinja2
-    types-PyYAML
-    types-Werkzeug
-    types-click
-    types-pkg_resources
 commands =
     # No where close to passing yet, but nice to have.
-    - mypy --junit-xml=junit-{envname}.xml --py2 --ignore-missing-imports lnt
-    - mypy --junit-xml=junit-{envname}.xml --ignore-missing-imports lnt
+    - mypy --install-types --non-interactive --junit-xml=junit-{envname}.xml --py2 --ignore-missing-imports lnt
+    - mypy --install-types --non-interactive --junit-xml=junit-{envname}.xml --ignore-missing-imports lnt
 
 [testenv:flake8]
 skip_install = true