scripts/genproto: use latest "grpc-ecosystem/grpc-gateway"

scripts/genproto.sh

@@ -20,7 +20,7 @@ DIRS="./wal/walpb ./etcdserver/etcdserverpb ./etcdserver/api/snap/snappb ./raft/
 
 # exact version of packages to build
 GOGO_PROTO_SHA="1adfc126b41513cc696b209667c8656ea7aac67c"
-GRPC_GATEWAY_SHA="74ba57806b9706edc6e2c9e5854ced57a9cd5ba0"
+GRPC_GATEWAY_SHA="92583770e3f01b09a0d3e9bdf64321d8bebd48f2"
 SCHWAG_SHA="b7d0fc9aadaaae3d61aaadfc12e4a2f945514912"
 
 # set up self-contained GOPATH for building