fix #12261
mark .box-shadow() mixin as deprecated; fixes #12396
docs & comments: v3.1 => v3.1.0
Merge pull request #12398 from twbs/deprecate-box-shadow-mixin

mark .box-shadow() mixin as deprecated
Merge pull request #12315 from twbs/use-shrinkwrap

Do npm caching based on npm-shrinkwrap.canonical.json