Make workbox-build exist in jsdoc
Make workbox-build exist in jsdoc

All workbox-build docs currently hang off of workbox-build module in jsdocs, but that module was never defined which meant the docs have just been lost.
This adds the module to jsdocs but the actual document seems pretty wrong.
GoogleChrome/workbox,GoogleChrome/workbox,GoogleChrome/workbox,GoogleChrome/workbox