Modified plugin.json to suppress annoying deprecation warning and file not found warning.

warn: [plugins/nodebb-plugin-dailymotion] staticDir is deprecated, use staticDirs instead
warn: [meta/css] File not found! nodebb-plugin-dailymotion/style.css
Merge pull request #1 from opt9/master

Modified plugin.json to suppress annoying deprecation warning and file not found warning.