Workaround mangled javadocs

The current build fails when executing <tt>gradle install</tt> with the following message:

    [...]
    100 errors
    100 warnings
    :javadoc FAILED
    
    FAILURE: Build failed with an exception.
    
    * What went wrong:
    Execution failed for task ':javadoc'.
    [...]

In my opinion, the javadocs are too mangled to try to fix them. This workaround allows the build to ignore javadoc errors when installing artifacts.