Bug#939881: FTBFS: trying to run :rabbitmqctl on Elixir v1.9.1 but supports only >= 1.6.6 and < 1.8.0

[Ryan Tandy]

Control: tag -1 fixed-upstream

Elixir 1.9 is supported in upstream version 3.7.16 and later (current is 
3.7.17).

https://github.com/rabbitmq/rabbitmq-cli/compare/v3.7.15...v3.7.16
https://github.com/rabbitmq/rabbitmq-cli/commit/c3c6b9edd5af947c69370658f609026bfef8055b