Run install checck only on master

.drone.yml

@@ -158,6 +158,9 @@ steps:
        [ $(python -c "import lmwsip; print(lmwsip.__version__)") =
        $(python setup.py --version) ]
       - python -m unittest -v lmwsip.tests
+    when:
+      branch:
+        - master
 
 depends_on:
   - Build