phabricator: properly encode boolean types in the request body I tripped over this playing with `hg debugcallconduit` to query for valid reviewers. If the JSON on stdin is written as 'True' or 'False', python complains it isn't valid JSON. If it's written as 'true' or 'false', it made it to the server, but got kicked back with this: abort: Conduit Error (ERR-CONDUIT-CORE): Error while reading "isBot": Expected boolean (true or false), got something else. The test isn't really relevant here (the code can be reverted, and it will pass), but this gives us coverage for the debug command.