Use "Returns:" to annotate return values

To be able to annotate return values through GObject-introspection, you
need to make sure it is tagged with `Returns:` and not something else.

libgimpwidgets/gimpcairo-utils.c

@@ -50,7 +50,7 @@
  * Sets color and dash pattern for stroking a focus line on the given
  * @cr. The line pattern is taken from @widget.
  *
- * Return value: %TRUE if the widget style has a focus line pattern,
+ * Returns: %TRUE if the widget style has a focus line pattern,
  *               %FALSE otherwise
  *
  * Since: 2.6