make sure flake8 is installed

add tag condition

Author: Vladimir Kotal

.travis.yml

@@ -39,6 +39,8 @@ jobs:
       install: true
     - stage: deploy
       name: Github Release
+      if: tag IS present
+      before_install: dev/before_install
       script: mvn -DskipTests=true -Dmaven.javadoc.skip=false -B -V package
       deploy:
         # Pre-release