Update screenshot with Firefox and Chrome

README.md

@@ -22,7 +22,7 @@ Created a new certificate valid for the following names 📜
 The certificate is at "./example.com+5.pem" and the key at "./example.com+5-key.pem" ✅
 ```
 
-<p align="center"><img width="444" alt="Chrome screenshot" src="https://user-images.githubusercontent.com/1225294/41887838-7acd55ca-78d0-11e8-8a81-139a54faaf87.png"></p>
+<p align="center"><img width="498" alt="Chrome and Firefox screenshot" src="https://user-images.githubusercontent.com/1225294/51066373-96d4aa80-15be-11e9-91e2-f4e44a3a4458.png"></p>
 
 Using certificates from real certificate authorities (CAs) for development can be dangerous or impossible (for hosts like `localhost` or `127.0.0.1`), but self-signed certificates cause trust errors. Managing your own CA is the best solution, but usually involves arcane commands, specialized knowledge and manual steps.