Don't replace colons with '=' inside attribute values

[Josh Adams]

The following:

%img{src: "http://placehold.it/80x80&text=[img]" }

gets parsed into:

<img src="http=//placehold.it/80x80&text=[img]" />

Notice the = instead of : inside the src attribute.

[Johnny Winn]

Done! Changes are in master

[Josh Adams]

Woot!