bootstrap.native: Any instance of the string 'in' in a collapse's class attribute breaks Collapse

@thednp BS v4’s css will be totally broken in IE9, why support IE9 for the JS?

this issue still isn’t fixed.

1. \bin: http://regexr.com/3euta 2. \bin\b: http://regexr.com/3eutm 3. (^|\s)in($|\s): http://regexr.com/3eutg

1. matches words like navbar-inverse-collapse and inverse-class
2. matches words like navbar-in-example
3. checks if string begins in or there is a space before in, and ensures that either string ends with in or a space comes after.

edit: cc @thednp @lcannon