Fix the unban method
Fix the unban method

Which didn't work because of
https://github.com/matrix-org/synapse/issues/1860

matrix-org/matrix-js-sdk,krombel/matrix-js-sdk,krombel/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk