Redirect an old png badge with a number as a color; test on [static] (#3412)

Fixes https://github.com/badges/shields/issues/3260

Problem happens when a value of a color in an old PNG static badge is a number: http://localhost:8080/my-label/my-message.png?color=1. In this case `color` in `queryParams` is a number. 
0a0b5b3f03/core/server/server.js (L203-L212)

Surprisingly service test listed below is passing currently on master - value `1` is represented in `queryParams` as a String (only in test). 
`services/static-badge/static-badge.tester.js`
```js
t.create('Old static badge with a number as a color')
  .get('/foo/bar.png?color=1', { followRedirect: false })
  .expectStatus(301)
  .expectHeader('Location', '/badge/foo-bar-1.png')
```

Moreover I added some code + description allowing to debug server.

.vscode/launch.json

@@ -0,0 +1,13 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "type": "node",
+      "request": "attach",
+      "name": "Node: Nodemon",
+      "processId": "${command:PickProcess}",
+      "restart": true,
+      "protocol": "inspector"
+    }
+  ]
+}

README.md

@@ -111,6 +111,9 @@ To debug a badge from the command line, run `npm run badge -- /npm/v/nock.svg`.
 It also works with full URLs like
 `npm run badge -- https://img.shields.io/npm/v/nock.svg`.
 
+Use `npm run debug:server` to start server in debug mode.
+[This recipe][nodemon debug] shows how to debug Node.js application in [VS Code][].
+
 Shields has experimental support for [Gitpod Beta][gitpod], a pre-configured development
 environment that runs in your browser. To use Gitpod, click the button below and
 sign in with GitHub. Gitpod also offers a browser add-on, though it is not required.
@@ -137,6 +140,8 @@ Daily tests, including a full run of the service tests and overall code coverage
 [sentry configuration]: doc/self-hosting.md#sentry
 [daily-tests]: https://github.com/badges/daily-tests
 [nodemon]: https://nodemon.io/
+[nodemon debug]: https://github.com/Microsoft/vscode-recipes/tree/master/nodemon
+[vs code]: https://code.visualstudio.com/
 
 ## Hosting your own server
 

core/server/server.js

@@ -207,7 +207,8 @@ module.exports = class Server {
       const redirectUrl = staticBadgeUrl({
         label,
         message,
-        color,
+        // Fixes https://github.com/badges/shields/issues/3260
+        color: color ? color.toString() : undefined,
         format: 'png',
       })
 

package.json

@@ -107,6 +107,7 @@
     "now-start": "npm run start:server:prod",
     "start:server:e2e-on-build": "node server 8080",
     "start:server": "cross-env NODE_CONFIG_ENV=development nodemon server 8080",
+    "debug:server": "cross-env NODE_CONFIG_ENV=development nodemon --inspect server.js 8080",
     "prestart": "run-s --silent depcheck defs features",
     "start": "concurrently --names server,frontend \"npm run start:server\" \"cross-env GATSBY_BASE_URL=http://localhost:8080 gatsby develop --port 3000\"",
     "e2e": "start-server-and-test start http://localhost:3000 test:e2e",

services/static-badge/static-badge.tester.js

@@ -62,3 +62,8 @@ t.create('Old static badge')
   .get('/foo/bar.png?color=blue', { followRedirect: false })
   .expectStatus(301)
   .expectHeader('Location', '/badge/foo-bar-blue.png')
+
+t.create('Old static badge without a color')
+  .get('/foo/bar.png', { followRedirect: false })
+  .expectStatus(301)
+  .expectHeader('Location', '/badge/foo-bar-lightgray.png')