Remove stray comma.

It was creating an event with the file field looking like this:

    "file" => [
        [0] "?:?",
        [1] "?"
    ]

Now it looks like:

    "file" => "?:?"
Merge pull request #612 from bodgit/log4j

Remove stray comma in log4j input.

Conflicts:
	lib/logstash/inputs/log4j.rb