paket: fix build by requiring new MSBuild.StructuredLogger

AppVeyor was failing[1] with (which seemed to be same issue as
this one: [2]):

Script reported an error:
-> BuildFailedException: Target 'Build' failed.
-> One or more errors occurred. (Unsupported log file format. Latest supported version is 9, the log file has version 13.)
-> NotSupportedException: Unsupported log file format. Latest supported version is 9, the log file has version 13

[1] https://ci.appveyor.com/project/sergey-tihon/fsharpx-collections/builds/40656359
[2] fsprojects/FAKE#2595