Add ESLint. Related d3/d3-scale#59.

Author: mbostock

.eslintrc

@@ -1,5 +1,5 @@
-ecmaFeatures:
-    modules: true
+parserOptions:
+    sourceType: "module"
 
 env:
     es6: true

package.json

@@ -30,8 +30,9 @@
     "d3-color": "~0.4.0"
   },
   "devDependencies": {
+    "eslint": "2",
     "json2module": "0.0",
-    "rollup": "0.25",
+    "rollup": "0.26",
     "tape": "4",
     "uglify-js": "2"
   }