version: fix documentation.
// ExtraGitCommit, if non-empty, is the git commit of a "supplemental"
// repository at which Tailscale was built. Its format is the same as
-// GitRevision.
+// gitCommit.
//
-// ExtraGitRevision is used to track the source revision when the main
+// ExtraGitCommit is used to track the source revision when the main
// Tailscale repository is integrated into and built from another
// repository (for example, Tailscale's proprietary code, or the
-// Android OSS repository). Together, GitRevision and ExtraGitRevision
+// Android OSS repository). Together, GitCommit and ExtraGitCommit
// exactly describe what repositories and commits were used in a
// build.
const ExtraGitCommit = ""
