Example fixture certificate is expired

[jakekreider]

The certificate expired on 4/22. Looks like it was last regenerated with #1594 .

% curl https://raw.githubusercontent.com/notaryproject/notary/master/fixtures/notary-server.crt | openssl x509 -noout -text
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  3883  100  3883    0     0  16125      0 --:--:-- --:--:-- --:--:-- 16594
Certificate:                                                                                                                 
    Data:                                                                                                                    
        Version: 3 (0x2)                                                                                                     
        Serial Number: 9243224537344790703 (0x804687be779c50af)                                                              
    Signature Algorithm: sha256WithRSAEncryption                                                                             
        Issuer: C=US, ST=CA, L=San Francisco, O=Docker, CN=Notary Intermediate Testing CA                                    
        Validity                                                                                                             
            Not Before: Apr  2 13:09:33 2021 GMT                                                                             
            Not After : Apr 22 13:09:33 2023 GMT