fixed build script

Build/build.ps1

@@ -3,8 +3,7 @@ param([string]$version)
 if ([string]::IsNullOrEmpty($version)) {$version = "0.0.1"}
 
 $msbuild = "MSBuild.exe"
-&$msbuild ..\Frameworks\MQTTnet.NetFramework\MQTTnet.NetFramework.csproj /t:Build /p:Configuration="Release"
-&$msbuild ..\Frameworks\MQTTnet.Netstandard\MQTTnet.Netstandard.csproj /t:Build /p:Configuration="Release"
+&dotnet build ..\Frameworks\MQTTnet.Netstandard\MQTTnet.Netstandard.csproj -c="Release"
 &$msbuild ..\Frameworks\MQTTnet.UniversalWindows\MQTTnet.UniversalWindows.csproj /t:Build /p:Configuration="Release"
 
 Remove-Item .\NuGet -Force -Recurse