Create branch-specific build process Travis file for Greenkeeper

[kylemh]

Feature

Why is this feature being added?

#118

I can't use yarn --pure-lockfile in CI with Greenkeeper involved, but it's the purest way to ensure the repository and CI environments have matching dependencies.

What should your feature do?

Use yarn --silent should run for all branches that include "greenkeeper/" in the branch name and yarn --pure-lockfile --silent should run otherwise.

[takethefake]

will do

[kylemh]

I am assigning myself to this issue as a placeholder for your work. Thank you, and good luck! 😁

Please note:
If no activity is shared within two weeks, I will remove my assignment. At that point, the issue will be open for anybody to take.

[kylemh]

Gonna reopen this issue as #201 silenced Greenkeeper and was reverted.