change TravisCI build (#245)

* use mvn clean verify

* deactivate findbugs

* limit push builds to master branch

* revert to "clean test"

.travis.yml

@@ -1,9 +1,12 @@
+branches:
+  only:
+  - master
 language: groovy
 sudo: false
 install:
 - pip install --user mkdocs==0.17.5 mkdocs-material==2.9.4
 script:
-- mvn test -B
+- mvn clean test --batch-mode
 - |
   if [[ "${TRAVIS_PULL_REQUEST}" != "false" ]]
   then

pom.xml

@@ -38,6 +38,7 @@
     </pluginRepositories>
 
     <properties>
+        <findbugs.skip>true</findbugs.skip>
         <jenkins.version>2.32.3</jenkins.version>
         <pipeline.version>2.5</pipeline.version>
         <cps.global.lib.version>2.6</cps.global.lib.version>