Allow any default parameter in two-fer

[skeltoac]

Fixes #431

[jiegillet]

Hi @skeltoac, thank you for the PR.
While I believe that using "you" as the default parameter is the best way of solving the exercise, it's true that the comment is not accurate, so I'm OK with your proposed change.

That being said, could you:

1. Fix the failing test intest/elixir_analyzer/test_suite/two_fer_test.exs (basically remove the line 94 test)
2. Add a new test test_exercise_analysis "accepts any value as the default parameter" (with the line 94 test, the intended solution and maybe an extra one with an atom or something)

[jiegillet]

Nice! Thanks a lot :)