Correct schema for network-traffic http-request-ext request_header

[JasperJuergensen]

The STIX2.1 standard states for network-traffic http-request-ext request_header:

The corresponding value for each dictionary key MUST always be a list of type string to support when a header field is repeated.

The JSON schema now adheres to that specification.

Closes #152

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[rpiazza]

Can we merge this even though the CLA isn't signed?

[clenk]

The email address used to create the commit doesn't match the email address of the github.com account. If there's a way to check the list of people who signed the CLA, you could see if the github.com account signed it.

[rpiazza]

Send email to Chet Ensign

[JasperJuergensen]

I haven't signed it. The reason is, that the work was done during working hours and therefor my employer might have some ownership on intellectual property (IP) rights. We (my employer and I) tried to sign a joined version of the CLA, but that failed due to some problems on oasis side. As both, my employer and the ownership of the IP rights have changed, we will not get such joined CLA agreement. I can offer to sign the CLA personally (so all rights I can personally grant are covered), but as I'm not a lawyer, I cannot grantee that's enough (I highly doubt the owner of the IP will do anything, but you never know). Only other option would either be to accept it without CLA or someone needs to rebuild it and create a new PR.