Fix bad relative hyperlink to features page

[bburhans]

Apologies if this is incorrect; I think it's accurate based on the assemble-generated paths on the actual web site, ignoring the very broken github markdown viewer paths.

[matthew-dean]

ignoring the very broken github markdown viewer paths

Explain?

[bburhans]

Relative URLs in markdown links are relative to a different base URL when rendered on github, because of the use of the assemble static site generator.

http://lesscss.org/functions/#logical-functions-if has a link to features/#mixins-feature-mixin-guards-feature which points to http://lesscss.org/functions/features/#mixins-feature-mixin-guards-feature, which does not exist. On github, it would point to yet another broken link either way. This pull simply fixed the former and ignored the latter, because this project does not and should not care about browsing the docs directly from github, correct?

[seven-phases-max]

Closing as done in f5c5f8b (Though I'm still not sure what would be the proper way to write such links... Could be also ../features...?)