Add eslint

package.json

@@ -7,7 +7,8 @@
   "types": "dist/src/index.d.ts",
   "scripts": {
     "test": "jest",
-    "build": "tsc"
+    "build": "tsc",
+    "lint": "eslint"
   },
   "publishConfig": {
     "access": "public"
@@ -35,6 +36,7 @@
     "@types/koa-compose": "*",
     "@types/safe-compare": "^1.1.0",
     "babel-preset-shopify": "^21.0.0",
+    "eslint": "^7.8.1",
     "jest": "^26.4.2",
     "koa": "^2.5.0",
     "node-fetch": "^2.6.0",