electrum: 3.0.3 -> 3.0.4

From the release notes [1]:

 * Fix a vulnerability caused by Cross-Origin Resource Sharing (CORS)
   in the JSONRPC interface. Previous versions of Electrum are
   vulnerable to port scanning and deanonimization attacks from
   malicious websites. Wallets that are not password-protected are
   vulnerable to theft.

See this [2] for explanation.

[1] https://github.com/spesmilo/electrum/blob/3.0.4/RELEASE-NOTES
[2] https://github.com/spesmilo/electrum/issues/3374