tests: use github workflow for nbsp char check

Let's use a github workflow instead of travis for this.

With this commit we can get rid of Travis.
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>

.github/workflows/check-nbsp.yml

+name: check-nbsp
+on: [pull_request]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - run: if [[ -n $(grep --exclude-dir=.git -P "\xa0" -r .) ]]; then echo 'NBSP characters found'; exit 1; fi

.travis.yml

-language: python
-python:
-  - "3.6"
-  - "3.7"
-  - "3.8"
-notifications:
-  webhooks: https://galaxy.ansible.com/api/v1/notifications/
-install:
-  - pip install -r tests/requirements.txt
-script:
-  - if [[ -n $(grep --exclude-dir=.git -P "\xa0" -r .) ]]; then echo 'NBSP characters found'; exit 1; fi