Add bare minimum ESLint config file. (#33)

This allows `npm test` to execute eslint.

Author: aholmes

.eslintrc.json

@@ -0,0 +1,7 @@
+{
+  "parser": "@typescript-eslint/parser",
+  "parserOptions": {
+    "ecmaVersion": "latest",
+    "sourceType": "module"
+  }
+}