Explicitly depend on System.Runtime.CompilerServices.Unsafe 6.0.0

...for net4.x and netstandard2.x

Author: jstedfast

MailKit/MailKit.csproj

@@ -55,6 +55,10 @@
     <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.4" />
   </ItemGroup>
 
+  <ItemGroup Condition=" $(TargetFramework.StartsWith('net4')) Or $(TargetFramework.StartsWith('netstandard2.')) ">
+    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="6.0.0" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\submodules\MimeKit\MimeKit\MimeKit.csproj" />
   </ItemGroup>

MailKit/MailKitLite.csproj

@@ -60,6 +60,10 @@
     <PackageReference Include="System.Formats.Asn1" Version="8.0.1" />
   </ItemGroup>
 
+  <ItemGroup Condition=" $(TargetFramework.StartsWith('net4')) Or $(TargetFramework.StartsWith('netstandard2.')) ">
+    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="6.0.0" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\submodules\MimeKit\MimeKit\MimeKitLite.csproj" />
   </ItemGroup>