Update cluster-proportional-autoscaler version in FAQ (kubernetes#5098)

Author: jahands

cluster-autoscaler/FAQ.md

@@ -445,10 +445,10 @@ spec:
         app: overprovisioning-autoscaler
     spec:
       containers:
-        - image: k8s.gcr.io/cluster-proportional-autoscaler-amd64:1.1.2
+        - image: k8s.gcr.io/cluster-proportional-autoscaler-amd64:1.8.1
           name: autoscaler
           command:
-            - ./cluster-proportional-autoscaler
+            - /cluster-proportional-autoscaler
             - --namespace=default
             - --configmap=overprovisioning-autoscaler
             - --default-params={"linear":{"coresPerReplica":1}}