Fix unbound variable error in Elixir v1.5.0-dev

It's not clear to me why "e in _" ever worked, but this seems to make
things better. Afaict, the point of these clauses are to "rescue
anything".

lib/koans.ex

@@ -22,7 +22,7 @@ defmodule Koans do
           unquote(compiled_body)
           :ok
         rescue
-          e in _ -> e
+          e -> e
         end
       end
     end
@@ -37,7 +37,7 @@ defmodule Koans do
           unquote(single_var)
           :ok
         rescue
-          e in _ -> e
+          e -> e
         end
       end
     end
@@ -52,7 +52,7 @@ defmodule Koans do
           unquote(multi_var)
           :ok
         rescue
-          e in _ -> e
+          e -> e
         end
       end
     end