In consideration of a future v5, update minimum git version.

src/git-command-manager.ts

@@ -11,7 +11,8 @@ import {GitVersion} from './git-version'
 
 // Auth header not supported before 2.9
 // Wire protocol v2 not supported before 2.18
-export const MinimumGitVersion = new GitVersion('2.18')
+// sparse-checkout not supported before 2.27
+export const MinimumGitVersion = new GitVersion('2.27')
 
 export interface IGitCommandManager {
   branchDelete(remote: boolean, branch: string): Promise<void>