Bump System.IO.Abstractions from 2.1.0.256 to 4.2.4 (#265)

Bumps [System.IO.Abstractions](https://github.com/System-IO-Abstractions/System.IO.Abstractions) from 2.1.0.256 to 4.2.4.
- [Release notes](https://github.com/System-IO-Abstractions/System.IO.Abstractions/releases)
- [Commits](https://github.com/System-IO-Abstractions/System.IO.Abstractions/commits/v4.2.4)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Fritz.StreamTools/Fritz.StreamTools.csproj

@@ -27,7 +27,7 @@
 		<PackageReference Include="Microsoft.Azure.CognitiveServices.Language.TextAnalytics" Version="2.8.0-preview" />
 		<PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="2.1.6" />
 		<PackageReference Include="Octokit" Version="0.32.0" />
-		<PackageReference Include="System.IO.Abstractions" Version="2.1.0.256" />
+		<PackageReference Include="System.IO.Abstractions" Version="4.2.4" />
 		<PackageReference Include="System.Memory" Version="4.5.2" />
 	</ItemGroup>
 	<ItemGroup>

Test/Test.csproj

@@ -13,7 +13,7 @@
     <PackageReference Include="FluentAssertions" Version="5.6.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.8.0-preview-20180610-02" />
     <PackageReference Include="Moq" Version="4.10.0" />
-    <PackageReference Include="System.IO.Abstractions" Version="2.1.0.256" />
+    <PackageReference Include="System.IO.Abstractions" Version="4.2.4" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1">
       <PrivateAssets>all</PrivateAssets>