add lint npm script

.eslintrc.json

@@ -22,6 +22,9 @@
     "arrow-spacing": 2,
     "no-inner-declarations": 0,
     "@typescript-eslint/indent": [2, "tab", { "SwitchCase": 1 }],
+    "@typescript-eslint/explicit-function-return-type": ["error", {
+      "allowExpressions": true
+    }],
     "@typescript-eslint/camelcase": "off"
   },
   "env": {

package.json

@@ -35,7 +35,8 @@
     "prepublishOnly": "export PUBLISH=true && npm test && npm run create-stubs",
     "create-stubs": "node scripts/create-stubs.js",
     "tsd": "tsc -p . --emitDeclarationOnly",
-    "typecheck": "tsc -p . --noEmit"
+    "typecheck": "tsc -p . --noEmit",
+    "lint": "eslint \"{src,test}/**/*.{ts,js}\""
   },
   "repository": {
     "type": "git",