Merge pull request #2183 from yui-knk/fix-error-comment

Fix comment of exc_inspect (and adjust spaces)

src/error.c

@@ -115,7 +115,10 @@ exc_message(mrb_state *mrb, mrb_value exc)
  * call-seq:
  *   exception.inspect   -> string
  *
- * Return this exception's class name an message
+ * Returns this exception's file name, line number,
+ * message and class name.
+ * If file name or line number is not set,
+ * returns message and class name.
  */
 
 static mrb_value