added 2.6 to .NET build
added 2.6 to .NET build

JetBrains/teamcity-nuget-support,stormleoxia/teamcity-nuget-support,JetBrains/teamcity-nuget-support,JetBrains/teamcity-nuget-support,JetBrains/teamcity-nuget-support,stormleoxia/teamcity-nuget-support,stormleoxia/teamcity-nuget-support