Specify exact version of highlights dependency
Specify exact version of highlights dependency

The newest 1.x version of highlights uses a version of first-mate
that does not work with old versions of node/npm.

Signed-off-by: Nathan Sobo <2e8aa918660411855c6d44d5bb2da677aa033255@github.com>

grimmer0125/markdown-preview-kramdown,atom/markdown-preview