chore(AIP-162): align example request message name with Alias method (#1409)

Author: jorgebarmza

aip/general/0162.md

@@ -112,7 +112,7 @@ APIs **may** provide a mechanism for users to assign an [alias][] ID to an
 existing revision with a custom method "alias":
 
 ```proto
-rpc AliasBookRevision(TagBookRevisionRequest) returns (Book) {
+rpc AliasBookRevision(AliasBookRevisionRequest) returns (Book) {
   option (google.api.http) = {
     post: "/v1/{name=publishers/*/books/*/revisions/*}:alias"
     body: "*"