Make the coverage report append rather than overwrite results

.gitlab-ci.yml

@@ -21,10 +21,11 @@ exitcode-jessie:
     - pip install -r requirements.txt
     - pip install coverage
     - pip install coverage-badge
-    - coverage run test/prior_tests.py
-    - coverage run test/tests.py
-    - coverage run test/waveform_generator_tests.py
-    - coverage run test/noise_realisation_tests.py
+    - coverage erase
+    - coverage run -a test/prior_tests.py
+    - coverage run -a test/tests.py
+    - coverage run -a test/waveform_generator_tests.py
+    - coverage run -a test/noise_realisation_tests.py
     - coverage html --include=peyote/*
     - coverage-badge -o coverage.svg
   artifacts: