Run against all RC versions of Immutable, and re-organize the Travis …

…config file a little

.travis.yml

@@ -11,9 +11,16 @@ os:
   - linux
   - osx
 
+matrix:
+  include:
+    - env: IMMUTABLE_VERSION=^4.0.0-rc
+
 install:
   - yarn install --frozen-lockfile
 
+before_script:
+  - if [ "$IMMUTABLE_VERSION" ]; then yarn add --dev immutable@$IMMUTABLE_VERSION; fi
+
 after_script:
   - if [[ "$TRAVIS_OS_NAME" == "linux" && "$TRAVIS_NODE_VERSION" == "11" ]]; then yarn coveralls; fi
 
@@ -22,13 +29,6 @@ notifications:
     on_success: never
     on_failure: always
 
-before_script:
-  - 'if [ "$IMMUTABLE_VERSION" ]; then yarn add immutable@$IMMUTABLE_VERSION; fi'
-
-matrix:
-  include:
-    - env: IMMUTABLE_VERSION=4.0.0-rc.12
-
 # Identifies `a.b.c-xxx.n` tags as pre-releases, and `a.b.c` as stable releases
 before_deploy: |
   function dist_tag() {