Merge pull request #786 from pascalberger/VSTSDocFix

Fix VSTS known limitation documentation

Author: gep13

docs/build-server-support/build-server/tfs-build-vnext.md

@@ -58,7 +58,7 @@ See [Variables](/more-info/variables/) for more info on the variables.
 * If you are using on premises TFS, make sure you are using at least **TFS 2015 Update 1**, otherwise a few things will not work.
 * You need to make sure that all tags are fetched for the Git repository, otherwise you may end with wrong versions (e.g. `FullSemVer` like `1.2.0+5` instead of `1.2.0` for tagged releases) 
 Just checking the `Clean Repository` check box in the build definition settings might not be enough since this will run a `git clean -fdx/reset --hard` without fetching all tags later. 
-You can force deletion of the whole folder and a re-clone containing all tags by settings the variable `Build.Clean` to `true`.
+You can force deletion of the whole folder and a re-clone containing all tags by settings the variable `Build.Clean` to `all`.
 This will take more time during build but makes sure that all tags are fetched.
 In the future it is planned to allow using `git.exe` instead of current `libgit2sharp` for syncing the repos which might allow other possibilities to solve this issue. 
 For details see this [GitHub issue](https://github.com/Microsoft/vso-agent-tasks/issues/1218).