travis.md

In the context of cljs-oss had success setting up Planck and triggering it to build with a specific version of ClojureScript. Here is a sketch:

1. I changed Planck's project.clj to have a dep that can be driven by an environment variable: [org.clojure/clojurescript ~(or (System/getenv "CLOJURESCRIPT_VERSION") "1.9.660")]
2. I added a minimal ".travis.yml-only" repo at https://github.com/cljs-oss/planck which clones and builds Planck and runs its tests
3. For the sake of running it in Travis, I forked this repo to my own GitHub account, but this step is just an optional pragmatic bit for now
4. I installed the travis client, logged in using a GitHub personal access token created for this purpose, and then had it give me a Travis API token
5. I chose which ClojureScript version I wanted to trigger the Planck build with: body='{"request": {"branch":"master", "config": {"env": {"CLOJURESCRIPT_VERSION": "1.9.671"}}}}'
6. I triggered the build: curl -s -X POST -H "Content-Type: application/json" -H "Accept: application/json" -H "Travis-API-Version: 3" -H "Authorization: token XXtokenhereXXXX" -d "$body" https://api.travis-ci.org/repo/mfikes%2Fplanck-1/requests
7. Observed the environment variable being set in the Travis web UI log: export CLOJURESCRIPT_VERSION=1.9.671
8. Confirmed that it was actually using this to build Planck by seeing WARNING: Use of undeclared Var cljs.js/lib at line 450 out/cljs/js.cljs which is in that version of ClojureScript