Ensure strip_html filter uses same regex as Ruby Liquid. Fixes #68

[paulrobertlloyd]

See the discussion in #68. I hope my tests are correct; I used " for my attribute test given the advice I found here.

[coveralls]

Coverage remained the same at 100.0% when pulling 2322e1d on paulrobertlloyd:master into f668a5c on harttle:master.

[aciccarello]

Should this handle tags on different lines?

The regex removes this:

<style type="text/css">.test-one-line {display: none;}</style>

But not this

<style type="text/css">
.test-one-line {display: none;}
</style>

I was able to workaround this issue by using joinLines before strip_html

[harttle]

@aciccarello please try v10.6.1

[aciccarello]

I've confirmed this is working as expected. Thanks!