Add standard linter

Author: watson

package.json

@@ -8,9 +8,11 @@
  "git-state": "^3.0.0",
  "minimist": "^1.2.0"
  },
- "devDependencies": {},
+ "devDependencies": {
+ "standard": "^8.1.0"
+ },
  "scripts": {
- "test": "echo \"Error: no test specified\" && exit 1"
+ "test": "standard"
  },
  "bin": {
  "git-att": "index.js"