Split up [github] testers (#2560)

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

services/github/github-commits-since.tester.js

@@ -0,0 +1,23 @@
+'use strict'
+
+const Joi = require('joi')
+
+const t = (module.exports = require('../create-service-tester')())
+
+t.create('Commits since')
+  .get('/badges/shields/a0663d8da53fb712472c02665e6ff7547ba945b7.json')
+  .expectJSONTypes(
+    Joi.object().keys({
+      name: Joi.string().regex(/^(commits since){1}[\s\S]+$/),
+      value: Joi.string().regex(/^\w+$/),
+    })
+  )
+
+t.create('Commits since by latest release')
+  .get('/microsoft/typescript/latest.json')
+  .expectJSONTypes(
+    Joi.object().keys({
+      name: Joi.string().regex(/^(commits since){1}[\s\S]+$/),
+      value: Joi.string().regex(/^\d+\w?$/),
+    })
+  )