generate unique certificate serial numbers (#1830)

Fixes browser errors thrown due to multiple certificates using the same issuer and serial number.  Occurs when a self-signed certificate has already been stored in the browser and new certificate is generated; either in the same project or across project installations.

src/utils/generateCertificate.js

@@ -27,7 +27,7 @@ function generateCertificate(options = {}) {
   const cert = pki.createCertificate();
 
   cert.publicKey = keys.publicKey;
-  cert.serialNumber = '01';
+  cert.serialNumber = Date.now().toString();
   cert.validity.notBefore = new Date();
   cert.validity.notAfter = new Date();
   cert.validity.notAfter.setFullYear(cert.validity.notBefore.getFullYear() + 1);