assemble/assemble-contrib-sitemap — pull request #6 by quartzmo (2013-12-11 16:38:40+00:00)
Title: Changed plugins: ['sitemap'] to plugins: ['assemble-contrib-sitemap'] in...

... README.

Assemble (0.4.31) did not find the plugin 'sitemap' (silent failure), but changing the name of the plugin to match the npm module resulted in the plugin running successfully.