Update for RabbitMQ 3.7

[youngj]

When trying to build and run the plugin on RabbitMQ 3.7, I encountered two issues:

• make dist failed with the error: erlang.mk:6513: recipe for target '/root/rabbitmq-auth-backend-ip-range/.erlang.mk/list-deps.log' failed
• After fixing the compilation issue (or after downloading the pre-compiled .ez file from https://dl.bintray.com/rabbitmq/community-plugins/3.7.x/rabbitmq_auth_backend_ip_range) and installing it in /usr/lib/rabbitmq/plugins, rabbitmq-plugins list did not detect the plugin and rabbitmq-plugins enable rabbitmq_auth_backend_ip_range failed

Replacing erlang.mk with the version from https://github.com/rabbitmq/rabbitmq-metronome fixed the issue with make dist.

Adding rabbit_common,rabbit,amqp_client into the applications section of rabbitmq_auth_backend_ip_range.app.src (to match rabbitmq-metronome) fixed the issue with rabbitmq-plugins not detecting the plugin.

According to http://erlang.org/doc/man/app.html, the mod section of the app file is not necessary ("mod can be omitted for applications without processes, typically code libraries, for example, STDLIB."), so I removed the mod section and rabbit_auth_backend_ip_range_app.erl

Changed the version number from 0.2.0 to 3.7.0 since it seems that other plugins use the version of RabbitMQ that they are built for as their own version number.

Built, installed and tested on Debian 9 with RabbitMQ 3.7.4.

[lukebakken]

Thanks! I have incorporated your changes into PR #8. When it's ready I will let you know and you can test.