update doc.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@34494 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

enum.c

@@ -445,7 +445,7 @@ flat_map_i(VALUE i, VALUE ary, int argc, VALUE *argv)
  *
  *  If no block is given, an enumerator is returned instead.
  *
- *     [[1, 2], [3, 4]].flat_map { |i| i }   #=> [1, 2, 3, 4]
+ *     [[1, 2], [3, 4]].flat_map { |e| e + [100] } #=> [1, 2, 100, 3, 4, 100]
  *
  */