Fix compilation on Erlang 19 by updating rebar.config

[TBK145]

The old exometer dependency had a lager dependency which did not compile on Erlang 19.

However, newer exometer versions do not have a lager dependency, so I had to add one manually, which fixed compilation on Erlang 19.

[TBK145]

It just occurred to me that this doesn't work. Apparently exometer (or hut for that matter) needs an extra flag to use lager. I'm trying to find out how that has to be done.

[TBK145]

It turns out I only had to add lager to the app.src

[surik]

Hi @TBK145, looks you use exometer_core revision with hut but there isn't capability to change the default log system without some hacks, see: https://github.com/Feuerlabs/exometer_core/issues/57

[TBK145]

I saw that there is some trouble with loggers, but with this pull request exometer still uses lager right?

[surik]

It uses hut and hut has a capability to change it via the compile flags (SASL error_logger used by default) but I don't see any ways to set these flags for exometer_core when I use it with other applications such as exometer_influxdb or so on.

I think you did some tests with the latest exometer_core and saw its log messages but probably they are just error_logger messages translated to lager, aren't they?

Please, correct me if I'm wrong.

[TBK145]

I'm not sure, but that might very well be possible.

[TBK145]

I currently have a workaround where I specify the newer lager dependency in my own project. Would it be a solution to add lager 3.2.1 as a dependency to this project and use the old exometer_core ref?

[surik]

Lets try

[TBK145]

I updated the PR, now it uses the same exometer_core commit as before, but lager 3.2.1 has been added as a dependency, so it compiles on Erlang 19.

[surik]

Good! Can you add some description about what you did it to overrided lager in rebar.config?

[surik]

And activate Erlang 19 in .travis.yml if it possible ;)

[TBK145]

I added a comment to rebar.config and added Erlang 19 to .travis.yml.

[surik]

Thank you!