GitVersionTask 5.0.1 does not work with MSBuild-14.0

[jbaehr]

When I reference the GitVersionTask in version 5.0.1 from a csproj I can't build it any more using MSBuild v14. It is the same error as in #1466, just another file: GitVersionTask/build/GitVersionTask.props. It appears that my fix for 4.0 (#1471) did not survive the commit 152de0d

Again, the issue is quite easy to fix: just add the namespace declaration to src/GitVersionTask/build/GitVersionTask.props:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
...

(the .target file misses the namespace declaration, too, but apparently msbuild does not care in that case)