Update html-minifier dependency version

[berniegp]

The html-minifier dependency is currently configured at 0.5.6.

New versions offer the ignoreCustomFragments option which allows minification to occur correctly in some underscore template use-cases.

For example:

<select>  <option value="1" <%= selected ? "selected" : "" %> ></option>  </select>

Does not parse properly with html-minifier 0.5.6. Newer versions have added the ignoreCustomFragments option which allows the minifier to ignore underscore template blocks. This can be used like so for the default underscore template syntax:

ignoreCustomFragments: [/<%[^%]*%>/]