fix CamelCase plugins fail

[cshehadi]

Documentation says to use CamelCase to set up plugins, but this widget expects underscore. So currently:

'clientPlugins' => ['fontFamily', 'fontSize'], // this causes an error
'clientPlugins' => ['font_family', 'font_size'], // this works

after this fix, you can use either CamelCase or underscore to define a plugin.