Fix namespace issue for BinarySecurityToken tag

[jeffcarbs]

In nokogiri 1.12.0 the following change was introduced:

[CRuby] Reparented nodes no longer inherit their parent's namespace. Previously, a node without a namespace was forced to adopt its parent's namespace. [https://github.com/sparklemotion/nokogiri/issues/1712, https://github.com/sparklemotion/nokogiri/issues/425]

It seems like the BinarySecurityToken was implicitly relying on this to add the wsse: prefix which is no longer happening. This PR fixes it by explicitly adding the namespace.

[bjensen]

👍

[jweir]

Running this patch against a test in our system works, but for some reason #31 is still producing a BinarySecurityToken tag without the namespace.

[ebeigarts]

@jweir I have released #31 in signer v1.10.0 and the tests are green now with nokogiri 1.12.5, please try signer v1.10.0 and reopen/rebase with test cases if there is still an issue.