Support `time-manager-0.3.*`

Tests are failing with `time-manager-0.3.*` (https://github.com/snoyberg/http-client/commit/be9b9c44b4eac65dba5c8803e018c295178392df). I don't know what exactly makes `time-manager-0.3.*` incompatible with previous versions. @kazu-yamamoto Can you help with fixing the tests?