Fixes #50 - package license not correctly marked

Author: nblumhardt

src/Serilog.Sinks.Async/Serilog.Sinks.Async.csproj

@@ -17,7 +17,7 @@
     <PackageTags>serilog;async</PackageTags>
     <PackageIconUrl>https://serilog.net/images/serilog-sink-nuget.png</PackageIconUrl>
     <PackageProjectUrl>https://serilog.net</PackageProjectUrl>
-    <PackageLicense>Apache-2.0</PackageLicense>
+    <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
     <RepositoryUrl>https://github.com/serilog/serilog-sinks-async</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
     <TreatWarningsAsErrors>True</TreatWarningsAsErrors>