Fix class filter

[nextgenthemes]

I was getting a $value not defined error and indeed the $value is never defined in that method. I also did not understand the $this->attr[ $name ] and figure you probably meant $this->attr['class'].

After this change the class filter works as expected.

[justintadlock]

Looks like I forgot to change things when I moved the hook outside of the foreach loop in another method.