Split up [github] testers (#2560)

- Update github contributors badge for `create-service-tester`.

services/github/github-size.tester.js

@@ -0,0 +1,18 @@
+'use strict'
+
+const Joi = require('joi')
+const { isFileSize } = require('../test-validators')
+
+const t = (module.exports = require('../create-service-tester')())
+
+t.create('File size')
+  .get('/webcaetano/craft/build/phaser-craft.min.js.json')
+  .expectJSONTypes(Joi.object().keys({ name: 'size', value: isFileSize }))
+
+t.create('File size 404')
+  .get('/webcaetano/craft/build/does-not-exist.min.js.json')
+  .expectJSON({ name: 'size', value: 'repo or file not found' })
+
+t.create('File size for "not a regular file"')
+  .get('/webcaetano/craft/build.json')
+  .expectJSON({ name: 'size', value: 'not a regular file' })