Tweak error in gradle

[sue445]

ref. http://stackoverflow.com/questions/10312259/recommended-way-to-stop-a-build-with-gradle

example

$ ./gradlew checkVersion
Picked up _JAVA_OPTIONS: -Dfile.encoding=UTF-8
Parallel execution with configuration on demand is an incubating feature.
:checkVersion FAILED

FAILURE: Build failed with an exception.

* Where:
Build file '/Users/sue445/dev/workspace/github.com/jenkinsci/yaml-axis-plugin/build.gradle' line: 78

* What went wrong:
Execution failed for task ':checkVersion'.
> Remove '-SNAPSHOT' of version!

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

Total time: 44.963 secs