Revert C# 7.1 dependency due to appveyor build issue
Revert C# 7.1 dependency due to appveyor build issue

JasonBock/csla,rockfordlhotka/csla,JasonBock/csla,MarimerLLC/csla,MarimerLLC/csla,MarimerLLC/csla,rockfordlhotka/csla,JasonBock/csla,rockfordlhotka/csla