Travis failue at checkstyle_regression_no_exception.sh "cannot get Checkstyle version from"

https://travis-ci.org/checkstyle/regression-tool/jobs/591464250#L35700

```
onfig generated at /home/travis/build/checkstyle/regression-tool/config-test-branch-20190930121503.xml
Installing Checkstyle artifact (master) into local Maven repository ...
Switched to branch 'master'
Your branch is behind 'origin/master' by 1 commit, and can be fast-forwarded.
(use "git pull" to update your local branch)
MSG:[maven-release-plugin] prepare release checkstyle-8.25
SHA-1:2f0c2f488a0d302bafe808e08ef47f691163c53b
Caught: groovy.lang.GroovyRuntimeException: Error: cannot get Checkstyle version from /home/travis/build/checkstyle/regression-tool/checkstyle/pom.xml!
groovy.lang.GroovyRuntimeException: Error: cannot get Checkstyle version from /home/travis/build/checkstyle/regression-tool/checkstyle/pom.xml!
at diff.getCheckstyleVersionFromPomXml(diff.groovy:174)
at diff$getCheckstyleVersionFromPomXml$8.callCurrent(Unknown Source)
at diff.generateCheckstyleReport(diff.groovy:184)
at diff$generateCheckstyleReport$5.callCurrent(Unknown Source)
at diff.run(diff.groovy:26)
Exception in thread "main" java.lang.IllegalStateException: an error occurred when running diff.groovy
at com.github.checkstyle.regression.report.ReportGenerator.generate(ReportGenerator.java:61)
at com.github.checkstyle.regression.Main.runRegression(Main.java:190)
at com.github.checkstyle.regression.Main.main(Main.java:111)

```