Make testsuite fail if coverage is under 100%

Fixes issue #61

.gitlab-ci.yml

@@ -44,7 +44,7 @@ tests:debian:
   - apt-get -qqy update
   - apt-get -qqy install --no-install-recommends python3-mutagen python3-gi-cairo gir1.2-poppler-0.18 gir1.2-gdkpixbuf-2.0 libimage-exiftool-perl python3-coverage
   - python3-coverage run --branch -m unittest discover -s tests/
-  - python3-coverage report -m --include 'libmat2/*'
+  - python3-coverage report --fail-under=100 -m --include 'libmat2/*'
 
 tests:fedora:
   image: fedora