[SPARK-4193][BUILD] Disable doclint in Java 8 to prevent from build error.

@ueshin One last tiny thing. I think this plugin should be declared in `<pluginManagement>`, and should add `<version>2.10.1</version>`, but would not have `<configuration>` of course. Then this is left exactly as-is.

All -- I think this may help the problem in SPARK-4543? It is good to commit this fix anyway but may also simply silence Java 8's warnings on missing javadoc as desired.