.gitlab-ci.yml: install loguru before running tests

.gitlab-ci.yml

@@ -21,6 +21,7 @@ tests:
     - pip install lazyparser==0.2.0
     - pip install pyfaidx==0.5.7
     - pip install biopython==1.75
+    - pip install loguru==0.5.3
     - pip install flake8
   script:
     - coverage run -m unittest discover