[DOC] Fix a typo in dir.c

s/Retruns/Returns/

dir.c

@@ -3516,7 +3516,7 @@ file_s_fnmatch(int argc, VALUE *argv, VALUE obj)
  * call-seq:
  *   Dir.home(user_name = nil) -> dirpath
  *
- * Retruns the home directory path of the user specified with +user_name+
+ * Returns the home directory path of the user specified with +user_name+
  * if it is not +nil+, or the current login user:
  *
  *   Dir.home         # => "/home/me"