Update for release 1.19 in build.sh (#6299)

update versions in build.sh for new release

Author: gauron99

hack/build.sh

@@ -27,7 +27,7 @@ set -x
 # 1) Make a release-NN branch as normal.
 # 2) Update VERSIONS below (on main) to include the new version, and remove the oldest
 #    Order matters :-), Most recent first.
-VERSIONS=("1.18" "1.17" "1.16") # Docs version, results in the url e.g. knative.dev/docs-1.9/..
+VERSIONS=("1.19" "1.18" "1.17") # Docs version, results in the url e.g. knative.dev/docs-1.9/..
 # 4) PR the result to main.
 # 5) Party.