sw-build: globPatterns doesn't respect rootDirectory

[addyosmani]

Library Affected:
sw-build

Browser & Platform:
All browsers

Issue or Feature Request Description:
Reported via @arthurevans: when specifying a globPattern, users expect that they won't need to define the rootDirectory as part of the globPattern path - it should be the prefixed used. The current behavior will however not work. To fix that you need to manually prefix the root directory yourself:

swBuild.generateFileManifest({
  dest: './dist/precache-manifest.js',
  rootDirectory: './dist/',
-  globPatterns: ['dist/**'],
+  globPatterns: ['dist/**'],
  globIgnores: ['service-worker.js'],
})
.then(() => {
  console.log('File manifest has been created.');
});

I have verified this locally and ran into this bug in my own implementation over in ReactHN.

[jeffposnick]

Related: #358

[gauntface]

This should be fixed by #408