Chore: Improve travis matrix

Ensure we test with eslint 3.x, 4.x and 5.x, and node 10

Fixes #97

.travis.yml

@@ -1,15 +1,31 @@
 language: node_js
 cache: yarn
 node_js:
-  - "4"
-  - "6"
-  - "7"
-  - "8"
+  - "10"
   - "9"
+  - "8"
+  - "7"
+  - "6"
+  - "4"
 env:
-  - ESLINT_VERSION=latest
-  - ESLINT_VERSION=3.15.0
-before_script:
-  - if [[ $ESLINT_VERSION != "latest" ]]; then
+  - ESLINT_VERSION=current
+  - ESLINT_VERSION=^5
+  - ESLINT_VERSION=^4
+  - ESLINT_VERSION=^3
+matrix:
+  # ESLint 5 dropped support node v4 or v7
+  exclude:
+    - node_js: "7"
+      env: ESLINT_VERSION=current
+    - node_js: "4"
+      env: ESLINT_VERSION=current
+    - node_js: "7"
+      env: ESLINT_VERSION=^5
+    - node_js: "4"
+      env: ESLINT_VERSION=^5
+install:
+  - if [[ $ESLINT_VERSION != "current" ]]; then
     yarn upgrade "eslint@$ESLINT_VERSION";
     fi
+  - yarn install
+  - yarn run --silent eslint --version

package.json

@@ -36,7 +36,7 @@
   },
   "devDependencies": {
     "@not-an-aardvark/node-release-script": "^0.1.0",
-    "eslint": "^3.14.1",
+    "eslint": "^5.6.0",
     "eslint-config-not-an-aardvark": "^2.0.0",
     "eslint-config-prettier": "^1.3.0",
     "eslint-plugin-eslint-plugin": "^0.7.1",