Require node.js > 4.

.travis.yml

@@ -2,7 +2,7 @@
     "sudo": false,
     "dist": "trusty",
     "language": "node_js",
-    "node_js": ["8"],
+    "node_js": ["4", "8"],
     "before_install": [
         "if [[ `npm -v` != 5* ]]; then npm install -g npm@5; fi"
     ],
@@ -15,6 +15,9 @@
         "git clone --depth 1 https://github.com/twbs/bootstrap.git --branch v3-dev",
         "pushd bootstrap && jekyll build; popd"
     ],
+    "matrix": [
+        "fast_finish": true
+    ],
     "script": [
         "npm test",
         "./src/cli-main.js bootstrap/_gh_pages/**/index.html",

package.json

@@ -77,6 +77,9 @@
     "./src/cli-main.js": false,
     "./src/location.js": false
   },
+  "engines": {
+    "node": ">=4"
+  },
   "files": [
     "bin",
     "dist",