Bump AkkaVersion from 1.5.13 to 1.5.15 (#397)

* Bump AkkaVersion from 1.5.13 to 1.5.15

* Bump test target framework to net6.0

Author: Arkatufus

src/Directory.Build.props

@@ -11,7 +11,7 @@
     <!-- Visual Studio C# settings -->
     <NetFrameworkTestVersion>net472</NetFrameworkTestVersion>
     <NetStandardLibVersion>netstandard2.0</NetStandardLibVersion>
-    <NetCoreTestVersion>netcoreapp3.1</NetCoreTestVersion>
+    <NetCoreTestVersion>net6.0</NetCoreTestVersion>
   </PropertyGroup>
   <ItemGroup>
     <Using Include="Akka.Event" />

src/Directory.Packages.props

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
     <!-- Nuget package versions -->
-    <AkkaVersion>1.5.13</AkkaVersion>
+    <AkkaVersion>1.5.15</AkkaVersion>
     <!-- Unit test Nuget package versions -->
     <NBenchVersion>1.2.2</NBenchVersion>
     <TestSdkVersion>17.4.1</TestSdkVersion>
@@ -19,8 +19,8 @@
     <PackageVersion Include="EntityFramework" Version="6.4.4" />
     <PackageVersion Include="Akka.Hosting.TestKit" Version="$(AkkaVersion)" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
-    <PackageVersion Include="xunit" Version="2.5.1" />
-    <PackageVersion Include="xunit.runner.visualstudio" Version="2.5.1" />
+    <PackageVersion Include="xunit" Version="2.5.3" />
+    <PackageVersion Include="xunit.runner.visualstudio" Version="2.5.6" />
     <PackageVersion Include="Akka.TestKit.Xunit2" Version="$(AkkaVersion)" />
     <PackageVersion Include="Akka.Streams.TestKit" Version="$(AkkaVersion)" />    
     <PackageVersion Include="BenchmarkDotNet" Version="0.13.8" />