Breaking: Drop support for node v4, v7 and v9

Node v4, v7 and v9 are end of life and no longer supported.

Author: BPScott

.travis.yml

@@ -2,27 +2,13 @@ language: node_js
 cache: yarn
 node_js:
   - "10"
-  - "9"
   - "8"
-  - "7"
   - "6"
-  - "4"
 env:
   - 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";

package.json

@@ -49,7 +49,7 @@
     "vue-eslint-parser": "^2.0.2"
   },
   "engines": {
-    "node": ">=4.0.0"
+    "node": ">=6.0.0"
   },
   "license": "MIT"
 }

test/prettier.js

@@ -196,9 +196,6 @@ function loadInvalidFixture(name) {
  * @param {string} dir - Prettierrc fixture basename.
  * @returns {string} A javascript filename relative to the .prettierrc config.
  */
-function getPrettierRcJsFilename(dir, file) {
-  // Use default parameters when we drop support for node 4
-  file = typeof file !== 'undefined' ? file : 'dummy.js';
-
+function getPrettierRcJsFilename(dir, file = 'dummy.js') {
   return path.resolve(__dirname, `./prettierrc/${dir}/${file}`);
 }