Update to latest versions

[ejc123]

Updated Dockerfile to the latest Erlang 25.2.3.0 image

Updated dependencies:
Replaced rebar3_lfe_compile with rebar3_lfe (0.4.3) as the former was deprecated and points to the latter
Updated ltest to latest version 0.13.3
Updated lfe to latest version 2.1.1

All of the dependencies are available from hex.

I had to modify the expected_results.json files due to minor changes in the output. Things still passed/failed as expected. I also added a 'description' to each of the .app.src files to quiet a compiler warning.

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[ErikSchierboom]

Nice! Could you maybe also add a new test case that uses the old setup to see if that still works?

[ejc123]

I tried, but the old rebar.config will not work. There was a breaking change between rebar 3.15.x and 3.16 which breaks the old lfe-compile plugin.
It might be possible to install rebar 3.15.2 in docker, but Erlang versions newer than 19.0 will warn about removed functions that LFE 1.1.1 uses.
Not sure about the best path forward.

[ErikSchierboom]

Okay, then I would propose we do the following:

• Before merging this PR, we'll add rebar.config to an exercise's files.invalidator field in it's .meta/config.json file. Once this is merging, changing the rebar.config for an exercise will prompt a student to update, which we can then use to do a follow-up PR to update the exercises in the exercism/lfe repository to use the latest rebar.config. See https://github.com/exercism/scala/pull/735/files for an example of such a PR.
• After merging those two PRs, we can merge this.

[ejc123]

That's really slick. So nothing will change for students until the rebar.config changes are pushed? So rebar.lock would be updated in the same commit as rebar.config, correct?

[ejc123]

PR for adding rebar.config to exercise's files.invalidator field exercism/lfe#166

[ErikSchierboom]

So nothing will change for students until the rebar.config changes are pushed?

Well, if they would run their tests without updating their exercise, they would get an error. But they would be able to update their exercise via a simple process.

So rebar.lock would be updated in the same commit as rebar.config, correct?

Correct!

[ejc123]

This PR exercism/lfe#163 will update all the rebar.config and rebar.lock files.

The top-level documentation looks pretty good. There's a reference to a docker image in INSTALLATION.md which doesn't work for me, but I'm not sure if that's my setup or that it is 6 years old.
Would it be a good idea to remove this reference until an updated image is available?

[ErikSchierboom]

The top-level documentation looks pretty good. There's a reference to a docker image in INSTALLATION.md which doesn't work for me, but I'm not sure if that's my setup or that it is 6 years old.
Would it be a good idea to remove this reference until an updated image is available?

I think so.

[ejc123]

I updated INSTALLATION.md so exercism/lfe#163 is ready to go. Let me know if there are any other things that need to happen before these changes can be merged.
Otherwise I'll just let you merge things at your convenience.