fix a typo

[Charlie-Li-Code]

fix a typo

[CLAassistant]

All committers have signed the CLA.

[daohu527]

@Charlie-Li-Code Thanks for your interest in Apollo, We remind you that we should ensure that the format of the commit is consistent.

You can follow the docs in https://github.com/ApolloAuto/apollo/blob/master/CONTRIBUTING.md#commit-message