Fix expired certificate in e2e_test

[int128]

This will fix the failed test:

=== RUN   TestTLS
    server.go:36: oauth2cli: starting a server at 127.0.0.1:37285
    client.go:43: could not open browser request: could not send a request: Get "https://localhost:37285": x509: certificate has expired or is not yet valid: current time 2021-10-09T13:24:46Z is after 2020-09-23T10:33:00Z
2021/10/09 13:24:46 http: TLS handshake error from 127.0.0.1:42704: remote error: tls: bad certificate
    server.go:66: oauth2cli: shutting down the server
    server.go:70: oauth2cli: force-closing the server: shutdown failed: context deadline exceeded
    server.go:42: oauth2cli: stopped the server
    tls_test.go:69: could not get a token: authorization error: authorization error: context deadline exceeded
--- FAIL: TestTLS (1.00s)

I regenerated certificates using https://github.com/int128/kubelogin/blob/master/integration_test/keypair/testdata/Makefile.