Update CI procedure

.gitlab-ci.yml

@@ -5,32 +5,31 @@ stages:
   - coverage
   - doc
 
+before_script:
+    - make install
+
 test-py2:
     image: docker.km3net.de/base/python:2
     stage: test
     script:
-        - make install
         - make test
 
 test-py3.5:
     image: docker.km3net.de/base/python:3.5
     stage: test
     script:
-        - make install
         - make test
 
 test-py3.6:
     image: docker.km3net.de/base/python:3.6
     stage: test
     script:
-        - make install
         - make test
 
 test-py3.7:
     image: docker.km3net.de/base/python:3.7
     stage: test
     script:
-        - make install
         - make test
 
 code-style:
@@ -44,14 +43,12 @@ coverage:
     image: docker.km3net.de/base/python:3.6
     stage: coverage
     script:
-        - make install
         - "make test-cov|grep TOTAL| awk '{printf \"COVERAGE: %.2f%%\", (1-$3/$2)*100 }'"
     coverage: '/COVERAGE:\s*([0-9]*\.[0-9]*%)/'
     artifacts:
         paths:
             - reports/coverage
 
-
 pages:
     image: docker.km3net.de/base/python:3.6
     stage: doc