Output div generates invalid class code.

When generating a div for output of a graphviz_filter format, the format class is rendered incorrectly.

For example, if generating an SVG graph, the following div code is generated:

    <div class="graphviz graphviz-"svg>

This occurs because of a misplaced " in graphviz_filter.module on line 202:

      $output .= '<div class="graphviz graphviz-"'. $formats[$format]['format'] .'>';

Patch is attached.