update ONBUILD docs link to non-breaking link
@@ -136,7 +136,7 @@ In this case, the value of `FOO` environment variable will be set to `bar`.
In case you want to use one of the official Docker language stack images for
your build you don't have do anything extra. S2I is capable of recognizing the
-Docker image with [ONBUILD](https://docs.docker.com/reference/builder/#onbuild) instructions and choosing the OnBuild strategy. This
+Docker image with [ONBUILD](https://docs.docker.com/engine/reference/builder/#/onbuild) instructions and choosing the OnBuild strategy. This
strategy will trigger all ONBUILD instructions and execute the assemble script
(if it exists) as the last instruction.
