Fix broken link.

Closes #1827.

Author: chriseppstein

compass-style.org/content/reference/compass/helpers/color-stops.haml

@@ -20,7 +20,7 @@ documented_functions:
   .details
     %p
       The color-stops helper provides a way to pass an arbitrary number of
-      colors stops to the <a href="/reference/compass/css3/gradient/">gradient mixins</a>.
+      colors stops to the <a href="/reference/compass/css3/images/">gradient mixins</a>.
     %p
       Any number of comma-delimited color stops can be passed, each color stop
       should take the form of a color followed by an optional stopping point (separated by a space).