update findbugs to 3.0.0 to allow build with java8

without this build fails with "Unable to get XClass for java/lang/StringBuilder" ... due to findubs 2.5.4 not being compatible with java 8. With the change "mvn clean install" works fine.
Merge pull request #13 from rtack/patch-1

update findbugs to 3.0.0 to allow build with java8