Update README.md

Author: danielwertheim

README.md

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 # Ensure.That
 Ensure.That is a simple guard clause argument validation lib, that helps you with validation of your arguments.
 
-It's developed for .NET 4.5.1 as well as .NET Standard 1.1 and .NET Standard 2.0 and available via [NuGet](https://www.nuget.org/packages/ensure.that/).
+It's developed for .NET 4.5.2 as well as .NET Standard 1.1 and .NET Standard 2.0 and available via [NuGet](https://www.nuget.org/packages/ensure.that/).
 
 [![Build Status](https://dev.azure.com/daniel-wertheim/os/_apis/build/status/Ensure.That-CI?branchName=master)](https://dev.azure.com/daniel-wertheim/os/_build/latest?definitionId=1&branchName=master)
 [![NuGet](https://img.shields.io/nuget/v/ensure.that.svg)](http://nuget.org/packages/ensure.that)