Implicit funs shouldn't be counted as a level.

[jfacorro]

The following code warns about an expression past the nesting level of 3.

-module(hello).

f(X) ->
  case X of
    1 -> ok;
    _ ->
      case X of
        2 ->
          fun f/1;
        _ -> ok
      end
  end.

[jfacorro]

This can be fixed by changing the name of the nodes for implicit funs in ktn_code from inaka/erlang-katana.

[jfacorro]

When inaka/erlang-katana#130 is fixed and a new version is released we should update that in elvis_core and close this issue.