[BG-5699] Fix maximumSpendable call using send instead of query
[BG-5699] Fix maximumSpendable call using send instead of query

Summary: The platform is expecting parameters to maximumSpendable to be expressed as a query. The SDK was sending these parameters in the body, so they were being ignored.

Reviewers: arik, bigly, kevin

Reviewed By: kevin

Differential Revision: https://phabricator.bitgo.com/D9037

BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS