Add an ESLint configuration

This allows for convenient tab completion in VS Code, adapted from
https://github.com/git-for-windows/gfw-helper-github-app/blob/main/.eslintrc.json

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.eslintrc.json

@@ -0,0 +1,20 @@
+{
+  "env": {
+    "node": true,
+    "es6": true,
+    "jest/globals": true
+  },
+  "extends": "eslint:recommended",
+  "parserOptions": {
+    "ecmaVersion": 12,
+    "sourceType": "module"
+  },
+  "plugins": [
+    "jest"
+  ],
+  "root": true,
+  "rules": {
+    "indent": ["error", 4],
+    "no-trailing-spaces": "error"
+  }
+}

.vscode/settings.json

@@ -2,5 +2,8 @@
     "azureFunctions.deploySubpath": ".",
     "azureFunctions.projectLanguage": "JavaScript",
     "azureFunctions.projectRuntime": "~4",
-    "debug.internalConsoleOptions": "neverOpen"
+    "debug.internalConsoleOptions": "neverOpen",
+    "eslint.workingDirectories": [
+        "GitGitGadget"
+    ]
 }

GitGitGadget/index.js

@@ -1,4 +1,3 @@
-// @ts-check
 /*
  * This is the Azure Function backing the GitGitGadget GitHub App.
  *