Update version to 2.5.1

Test broker updates; VS2015 removal (#619)

* Test broker: single project for multiple framework targets

* Test broker: SASL anonymous by default

* Deprecate vs2015

* ci fix

* ci fix

* yml fix

* update

* update

* update

* update

Increase version to 2.4.11

Increase version to 2.4.10

Increase version to 2.4.9

Increase version to 2.4.8

Warnings in nuspec

Increase version to 2.4.6

Increase version to 2.4.5

Increase version to 2.4.3