Add netstandard1.1 and net40 targets to nuspec

LibVLCSharp.nuspec

@@ -19,6 +19,8 @@
     <file src="LibVLCSharp\bin\Release\monoandroid81\LibVLCSharp.Android.AWindow.dll" target="lib\MonoAndroid81"/>
     <file src="LibVLCSharp\bin\Release\xamarin.ios10\LibVLCSharp.dll" target="lib\Xamarin.iOS10"/>
     <file src="LibVLCSharp\bin\Release\netstandard2.0\LibVLCSharp.dll" target="lib\.NETStandard2.0"/>
+    <file src="LibVLCSharp\bin\Release\netstandard1.1\LibVLCSharp.dll" target="lib\.NETStandard1.1"/>
     <file src="LibVLCSharp\bin\Release\xamarin.mac20\LibVLCSharp.dll" target="lib\xamarinmac20"/>
+    <file src="LibVLCSharp\bin\Release\net40\LibVLCSharp.dll" target="lib\net40"/>
   </files>
 </package>
\ No newline at end of file

scripts/build-and-package-libvlcsharp.ps1

 $msbuild =  '"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\MSBuild.exe"'
-iex ("& {0} {1}" -f $msbuild, "../LibVLCSharp/LibVLCSharp.csproj /t:Build /p:Configuration=Release")
+iex ("& {0} {1}" -f $msbuild, "../LibVLCSharp/LibVLCSharp.csproj /t:Restore,Clean,Build /p:Configuration=Release")
 ..\nuget.exe pack ..\LibVLCSharp.nuspec
\ No newline at end of file