adds elm package install --yes to .travis.yml to install dependencies…

…! for dwyl/learn-travis#31

.travis.yml

@@ -1,6 +1,12 @@
-language: node_js
+sudo: false
+
+language: node_js # elm is installed from npm (see install below)
 node_js: node # use "latest" version of Node.js
 
+os: # test on *both* linux and OSX to ensure compatibility
+  - linux
+  - osx
+
 cache:
   directories: # so subsequent builds run faster
     - elm-stuff/build-artifacts
@@ -13,7 +19,7 @@ before_install:
   - if [ ${TRAVIS_OS_NAME} == "osx" ];
     then brew update; brew install nvm; mkdir ~/.nvm; export NVM_DIR=~/.nvm; source $(brew --prefix nvm)/nvm.sh;
     fi
-  - | # epic build time improvement - see https://github.com/elm-lang/elm-compiler/issues/1473#issuecomment-245704142
+  - | # epic build time improvement - 10 mins >> 5 sec! see https://git.io/vQcqz
     if [ ! -d sysconfcpus/bin ];
     then
       git clone https://github.com/obmarg/libsysconfcpus.git;
@@ -23,4 +29,7 @@ before_install:
       cd ..;
     fi
 install:
-  - npm install -g elm elm-test@0.18.6
+  - node --version # print Node.js version in Travis Log for debugging
+  - npm --version  # print npm version in Travis Log for debugging.
+  - npm install -g elm@0.18.0 elm-test@0.18.12 elm-format@exp
+  - elm package install --yes