PluginErrors

[strugee]

Properly use gulp PluginErrors across modules. https://github.com/gulpjs/gulp-util#new-pluginerrorpluginname-message-options

[strugee]

Here's a list of repositories we need to do this for:

• stratic-decorate-files
• stratic-date-in-path
• stratic-paginate-indexes
• stratic-indexes-to-rss
• stratic-posts-to-index
• stratic-filter-drafts
• gulp-attach-to-template
• stratic-default-categories
• stratic-truncate-indexes