Added one test to the polymorph suite (test name usage)

* added one tests that verifies that the diet function also
  accesses the name value of the map (before it was possible
  to just return "Bambi eats veggies." for the herbivore diet
* since this is not the main purpose of these specs added just
  this one and not extra specs for default/carnivore as I didn't
  want to bloat it, but could add those as well if desired
Move herbivore assertions together
Make if-not example clearer, fix the answer keys

I felt the example wasn't very clear as the conditional returned the
quoted form of `doom` when it evaluated to true or false. This way the
user needs to find a value that satisfies the if-not conditional so it
returns `doom` and not `more-doom`.
The answer file's expression returns the argument provided

Although the answer's file entry worked, it ignored the provided
argument. With this change it returns what was passed to it.  I branched
from master, I hope it can be merged it in.
Switch variable from index to x to avoid confusing syntax highlightig.

index is a clojure.set function and ended up highlighted for me, sending me
down a rabbit hole of confusion. Avoid this with a more generic variable name
consistent with other Koan files.
Update answer key to reflect renaming
group-by function koan
Clean up group-by descriptions & spelling
Remove group-by since that's been covered
Discourage lein 1 use