fix(bower-release): don't extend dependencies from source repository unless requested

It is now possible to request to extend the source repository's
dependencies, using the options key `extendDependencies` with the value
`true`.

This is not yet reflected in documentation. Unfortunately, the
infrastructure of this project is such that writing a test for this is very
difficult, so I'm just going to have to hope that it works.

I do hope to clean this up down the line, but you know how time is, fleeting.

Closes #31