CI: Simplify job definition

.travis.yml

@@ -1,45 +1,38 @@
 language: node_js
-
-node_js:
-  - "6"
-  - "8"
-  - "10"
+node_js: 10
 
 branches:
   except:
     - /^dependabot\/.*$/
 
-env:
-  - ESLINT_VERSION=2
-  - ESLINT_VERSION=3
-  - ESLINT_VERSION=4
-  - ESLINT_VERSION=5
-
-matrix:
-  exclude:
-  - node_js: "6"
-    env: ESLINT_VERSION=3
-  - node_js: "6"
-    env: ESLINT_VERSION=4
-  - node_js: "6"
-    env: ESLINT_VERSION=5
-  - node_js: "8"
-    env: ESLINT_VERSION=3
-  - node_js: "8"
-    env: ESLINT_VERSION=4
-  - node_js: "8"
-    env: ESLINT_VERSION=5
-
 cache:
   yarn: true
 
 before_install:
   - curl -o- -L https://yarnpkg.com/install.sh | bash
   - export PATH=$HOME/.yarn/bin:$PATH
 
-install:
-  - yarn install
-  - yarn add eslint@$ESLINT_VERSION
+jobs:
+  include:
+    - stage: test
+      install:
+        - yarn install
+
+    - &test
+      stage: test
+      node_js: 6
+      env: ESLINT_VERSION=2
+
+      install:
+        - yarn install
+        - yarn add eslint@$ESLINT_VERSION
+
+    - <<: *test
+      node_js: 8
+      env: ESLINT_VERSION=3
+
+    - <<: *test
+      env: ESLINT_VERSION=4
 
 deploy:
   provider: npm

package.json

@@ -30,7 +30,7 @@
   },
   "devDependencies": {
     "chai": "^4.2.0",
-    "eslint": "2.1.0",
+    "eslint": "5.7.0",
     "import-from": "^2.1.0",
     "mocha": "^5.2.0"
   },