docs(x/genutil): fix genesis migrate command examples (#22090)

(cherry picked from commit 8bbf51c)

x/genutil/client/cli/migrate.go

@@ -36,7 +36,7 @@ func MigrateGenesisCmd(migrations types.MigrationMap) *cobra.Command {
  Use: "migrate [target-version] [genesis-file]",
  Short: "Migrate genesis to a specified target version",
  Long: "Migrate the source genesis into the target version and print to STDOUT",
- Example: fmt.Sprintf("%s migrate v0.47 /path/to/genesis.json --chain-id=cosmoshub-3 --genesis-time=2019-04-22T17:00:00Z", version.AppName),
+ Example: fmt.Sprintf("%s genesis migrate v0.47 /path/to/genesis.json --chain-id=cosmoshub-3 --genesis-time=2019-04-22T17:00:00Z", version.AppName),
  Args: cobra.ExactArgs(2),
  RunE: func(cmd *cobra.Command, args []string) error {
  return MigrateHandler(cmd, args, migrations)