fix(release process): verify maven version number and paths

Author: KaiSchwarz-cnic

.travis.yml

@@ -25,13 +25,14 @@ branches:
     - /^dependabot.*$/
 before_install:
   - export MAVEN_OPTS=-Dorg.slf4j.simpleLogger.defaultLogLevel=WARN
-  - export M2_HOME=~/maven
+  - export M2_HOME=$HOME/maven
   - export PATH=${M2_HOME}/bin:${PATH}
 install:
   - travis_retry wget https://www-us.apache.org/dist/maven/maven-3/3.6.2/binaries/apache-maven-3.6.2-bin.tar.gz
   - tar -xvzf apache-maven-3.6.2-bin.tar.gz
   - sudo mv apache-maven-3.6.2 maven
 script:
+  - mvn -v
   - mvn -ntp site
   - mvn -ntp package
 jobs: