chore: add missing quotation mark (#664)

Source-Author: Bu Sun Kim <[email protected]>
Source-Date: Mon Jan 11 09:43:06 2021 -0700
Source-Repo: googleapis/synthtool
Source-Sha: 16ec872dd898d7de6e1822badfac32484b5d9031
Source-Link: https://github.com/googleapis/synthtool/commit/16ec872dd898d7de6e1822badfac32484b5d9031
2 files changed