Jenkins requires Java 8 so use compatible findbugs

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@1802364 13f79535-47bb-0310-9956-ffa450edef68

pom.xml

@@ -19,7 +19,7 @@
     <commons.logging.version>1.0.4</commons.logging.version>
     <compiler.plugin.version>3.1</compiler.plugin.version>
     <exec.plugin.version>1.4.0</exec.plugin.version>
-    <findbugs.plugin.version>2.5.5</findbugs.plugin.version>
+    <findbugs.plugin.version>3.0.4</findbugs.plugin.version>
     <jar.plugin.version>2.6</jar.plugin.version>
     <java.version>1.6</java.version>
     <junit.version>4.11</junit.version>