Add missing application tuple value for elli dependency

[oldgalileo]

It is possible that rebar incorrectly assumes the order of the dependencies necessary to compile. This will manifest itself in an error that resembels:

===> Compiling _build/default/lib/elli_cache/src/elli_middleware_cache.erl failed
_build/default/lib/elli_cache/src/elli_middleware_cache.erl:19: can't find include lib "elli/include/elli.hrl"
...

This is recognized in this post, where Fred Hobert explains that if a dependency isn't listed as a dependency in the application tuple, rebar3 does not guarantee the build order.

This change fixes this issue for rebar3.

[oldgalileo]

Also, Travis has been build-failing since Travis#20. It's not an issue with this PR specifically.

[fvasquez]

I know elli_cache is still pre-release but it sure would be nice if rebar3 could build it into our OTP applications.

[yurrriq]

Elli was deliberately not included in deps so users could/would have to provide their own version. Otherwise we might have mismatches and such. I wasn't aware of the rebar3 issue though. Thoughts, @elli-lib/team?

[tsloughter]

I think Fred is wrong about it needing to be in the application tuple to get the build order right. It has to be in either the app tuple or the deps list in order to get the build order right.

It may work with putting it only in the application's list of the .app.src. But not really any reason to not include it in the dpes list too I guess.

Rebar3 does dep resolving like maven, the first version it encounters during a sorted level walk of the dep tree is used, there can be no conflicts by the build system. So having it in the deps for the cache doesn't matter since the users version will override it.

[yurrriq]

👍 to adding elli to applications in elli_cache.app.src but not deps then, I think. Hopefully I get free time soon and can finish this..

[oldgalileo]

@yurrriq I've made the change and confirmed that keeping elli solely within the applications of the elli_cache.app.src works and resolves the issue.

[yurrriq]

LGTM, thanks!

[yurrriq]

PS I'd be happy to help review other PRs, as my time to actively contribute to this is nearly nonexitent for now.