TEST: add test for python 3.7

.gitlab-ci.yml

@@ -6,6 +6,11 @@ before_script:
   - pip install .
   - pip install pytest
 
+test37:
+  image: python:3.7
+  script:
+    - pytest gyral_structure/test -m "not slowtest"
+
 test36:
   image: python:3.6
   script: