fix kn download link (#297)

Author: ludovicmotte

documentation/modules/serving/pages/knative-client.adoc

@@ -21,7 +21,7 @@ At the end of this chapter you will be able to :
 [#kn-install]
 == Install
 
-Download the https://github.com/knative/client/releases/tag/{kn-client-version}[{kn-client-version}^] Knative Client and add it to your `PATH`.
+Download the https://github.com/knative/client/releases/tag/knative-{kn-client-version}[{kn-client-version}^] Knative Client and add it to your `PATH`.
 
 Verify installation by running the command: