Update dependencies

Also improve building a source distribution with poetry.
Also Reformat code for latest version of black.

Author: Cito

.travis.yml

@@ -24,7 +24,7 @@ cache:
     - "$HOME/.cache/pip"
     - "$TRAVIS_BUILD_DIR/.tox"
 install:
-  - pip install "poetry>=1.0.0"
+  - pip install "poetry>=1.1,<2"
   - poetry install
 script:
   - tox -e $TOXENV -- --cov-report term-missing --cov=graphql_relay
@@ -36,7 +36,7 @@ deploy:
   on:
     branch: master
     tags: true
-    python: 3.7
+    python: 3.8
   skip_existing: true
   username: mvanlonden
   password: