Configs are now expanded for hexo-util/highlight to make it easier to…

[alxbl]

This is part of the code necessary to address #2145.

It simply expands config.highlight inside of the options object that is passed to hexo-util/highlight.

I went this route to make sure that the plugin remains backward compatible for themes and people who have already styled based on the current highlight engine.

This is a quick proof of concept, and if everything is fine, I will update the documentation accordingly.

The other part of the PR will be in @hexojs/hexo-util

The matching PR to support the added highlight.hljs setting is located at hexo-util/#30

• Add test cases for the changes.
• Passed the CI test.

[alxbl]

Ah, I just realized why ...config wasn't being used... I hadn't noticed that node 6 support was required. In that case I can adjust the code to only extract the new setting into options or I can use Object.merge.

Let me know what course of action is best.

[coveralls]

Coverage decreased (-0.05%) to 97.176% when pulling 903e7df on alxbl:support-hljs into dee3b03 on hexojs:master.

[coveralls]

Coverage remained the same at 97.226% when pulling fa57d97 on alxbl:support-hljs into dee3b03 on hexojs:master.

[NoahDragon]

LGTM. Note for npm publishing, make sure this change deployed with hexojs/hexo-util#30 .