Bump markdown it to 3.0.7

3.0.7 / 2015-02-22

Match table columns count by header.
Added basic CLI support.
Added \v \f to valid whitespaces.
Use external package for unicode data (punctuation).

v0.12.0-v0.12.1 breaks paths in URL.

upgrade grunt-contrib-jshint to ~0.11.0
upgrade load-grunt-tasks to ~3.0.0

[skip validator]

Now, the zip file is created when running `grunt prep-release`.

[ci skip]

[skip sauce]

Fixes #15105.