drone/drone — pull request #746 by shawnzhu (2014-12-07 16:34:15+00:00)
Title: parse build file with params injection

the injected parameters like `$$HEROKU_TOKEN` doesn't work in `.drone.yml` (but works via environment variable `$HEROKU_TOKEN`).

Then I realized that when verifying #541, I just confirmed the new syntax `$$` within environment variable but not in `drone.yml` until today.