Fix missing word in garbage collection documentation

Author: JakobKohler

docs/snippets/about-revisions-garbage-collection.md

@@ -4,4 +4,4 @@
 -->
 When Revisions of a Knative Service are inactive, they are automatically cleaned up and cluster resources are reclaimed after a set time period. This is known as *[garbage collection](https://kubernetes.io/docs/concepts/architecture/garbage-collection/){target=_blank}*.
 
-You can configure garbage collection parameters a specific Revision if you are a developer. You can also configure default, cluster-wide garbage collection parameters for all the Revisions of all the Services on a cluster if you have cluster administrator permissions.
+You can configure garbage collection parameters for a specific Revision if you are a developer. You can also configure default, cluster-wide garbage collection parameters for all the Revisions of all the Services on a cluster if you have cluster administrator permissions.