Handle cert fingerprints that contain '/'

The cert fingerprint emitted by Muon/Electron is base64 encoded [1], so it may contain '/'. I think we were truncating the certificate fingerprint when this was the case, which may have caused the decoding error in #6524.

[1] https://cs.chromium.org/chromium/src/net/base/hash_value.h?q=net::HashValue&sq=package:chromium&l=58

Auditors: @darkdh

js/about/certerror.js

@@ -57,14 +57,16 @@ class CertErrorPage extends React.Component {
       var validExpiry = new Date()
       validStart.setTime(detail.validStart * 1000)
       validExpiry.setTime(detail.validExpiry * 1000)
+      var fingerprint = detail.fingerprint.split('/')
+      var algorithm = fingerprint.shift()
       this.setState({
         certDetail: true,
         certIssuerName: detail.issuerName,
         certSubjectName: detail.subjectName,
         certSerialNumber: seperateHex(detail.serialNumber),
         certValidStart: validStart.toString(),
         certValidExpiry: validExpiry.toString(),
-        certFingerprint: detail.fingerprint.split('/')
+        certFingerprint: [algorithm, fingerprint.join('/')]
       })
     })
   }