Don't set .me-plugin width/height to 0

While testing 2.15.0 for upgrade in WordPress, I noticed that all video files played by a plugin were only outputting audio, no video. Reverting https://github.com/johndyer/mediaelement/commit/53810f573dd7b16693e5d5a2cfa4375e4542935e returned playback to normal. In lieu of reverting, these values can just be changed to `auto`, so that the fix for IE8 will remain.