Update html-minifier dependency to fix some problems

In my use case, I want to use the collaspeWhitespace option to reduce the size of my templates but html-minifier 0.5.4 has some problems where it is a bit too greedy with collapsing whitespace. For example:
`html
<input type='checkbox' /> Foo
`
is minified to:
`html
<input type='checkbox'>Foo
`

Note the missing whitespace in front of Foo, this whitespace is significant with regards to styling and shouldn't be stripped; 0.6+ fixes this problem.