ci: tweaked caching settings

.travis.yml

@@ -1,8 +1,4 @@
 language: node_js
-node_js:
-- stable
-- lts/carbon
-- lts/boron
 sudo: false
 
 env:
@@ -14,24 +10,29 @@ before_install:
 - if [[ $GH_TOKEN ]]; then ./prepare-gpg-key.sh; fi;
 - greenkeeper-lockfile-update
 
-install: npm install
 script:
   - npm run tslint
   - npm test -- --forbid-only --forbid-pending
 after_script: if [[ $GH_TOKEN ]]; then greenkeeper-lockfile-upload; fi;
 after_success: cat ./coverage/lcov.info | coveralls
 
-before_cache: rm -rf ./node_modules/.cache
-cache:
-  directories:
-  - node_modules
-
 stages:
 - Test
 - Release
 
+oldNode: &oldNode
+  before_cache: rm -rf ./node_modules/.cache
+  cache:
+    directories:
+    - node_modules
+
 jobs:
   include:
+  - node_js: stable
+  - <<: *oldNode
+    node_js: lts/carbon
+  - <<: *oldNode
+    node_js: lts/boron
   - if: branch=master
     stage: Release
     node_js: stable