Update sinon dependency to version 20.0.

Author: diasbruno

package.json

@@ -58,7 +58,7 @@
     "react-router": "^4.2.0",
     "react-router-dom": "^4.2.2",
     "should": "^13.1.0",
-    "sinon": "next",
+    "sinon": "v20.0.0",
     "uglify-js": "3.1.1",
     "webpack": "^4.46.0",
     "webpack-cli": "^3.3.12",