Merge pull request protocolbuffers#9 from jtattermusch/add_system_memory_fixup2

 fixup2: add System.Memory dependency

Author: jtattermusch

csharp/src/Google.Protobuf/Google.Protobuf.csproj

@@ -6,7 +6,7 @@
     <AssemblyTitle>Google Protocol Buffers</AssemblyTitle>
     <VersionPrefix>3.6.0</VersionPrefix>
     <Authors>Google Inc.</Authors>
-    <TargetFrameworks>netstandard1.0;net45</TargetFrameworks>
+    <TargetFrameworks>netstandard1.1;net45</TargetFrameworks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <AssemblyOriginatorKeyFile>../../keys/Google.Protobuf.snk</AssemblyOriginatorKeyFile>
     <SignAssembly>true</SignAssembly>
@@ -30,7 +30,7 @@
 
   <ItemGroup>
     <PackageReference Include="SourceLink.Create.CommandLine" Version="2.7.6" PrivateAssets="All" />
-    <PackageReference Include="System.Memory" Version="4.5.1"/>
+    <PackageReference Include="System.Memory" Version="4.5.1" />
   </ItemGroup>
 
 </Project>