Builder for Libraries does not properly support recommend pattern for importing skyux assets

[Blackbaud-TomRamsey]

Expected behavior

@import "~@blackbaud/skyux/dist/scss/variables";

should work in an scss file in a skyux library

Actual behavior

uncaughtException: File to import not found or unreadable: ~@blackbaud/skyux/dist/scss/variables.

Steps to reproduce

1. Create a skyux library
2. Create an scss file, which uses "@import "~@blackbaud/skyux/dist/scss/variables";"
3. skyux build succeeds
4. skyux build-public-library fails

Workaround

@import "node_modules/@blackbaud/skyux/dist/scss/variables";