Add keywords to package.json

This will allow users to easier find the package at https://www.npmjs.com/search?q=keywords%3Atesting

Author: mroderick

package.json

@@ -1,6 +1,20 @@
 {
  "name": "sinon",
  "description": "JavaScript test spies, stubs and mocks.",
+ "keywords": [
+ "sinon",
+ "test",
+ "testing",
+ "unit",
+ "stub",
+ "spy",
+ "fake",
+ "time",
+ "clock",
+ "mock",
+ "xhr",
+ "assert"
+ ],
  "version": "9.2.3",
  "homepage": "https://sinonjs.org/",
  "author": "Christian Johansen",