Update SourceLink version.

Author: bgrainger

src/Directory.Build.props

@@ -19,7 +19,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0-beta-63127-02" PrivateAssets="All"/>
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0-beta2-18618-05" PrivateAssets="All"/>
   </ItemGroup>
 
   <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">