Bump System.Threading.Tasks.Extensions from 4.5.2 to 4.5.3 (#309)

Bumps [System.Threading.Tasks.Extensions](https://github.com/dotnet/corefx) from 4.5.2 to 4.5.3.
- [Release notes](https://github.com/dotnet/corefx/releases)
- [Commits](https://github.com/dotnet/corefx/commits)

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

Author: dependabot-preview[bot]

Fritz.StreamLib.Core/Fritz.StreamLib.Core.csproj

@@ -5,7 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.2" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.3" />
   </ItemGroup>
 
 </Project>