Fix NU5035 error with NuGet package license URL info. (#66)

X-ref: PR #63

ServerHost.sln

@@ -14,7 +14,6 @@ EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Build", "Build", "{64DBC33D-89B0-4F25-8E6D-3A4FAA8F4AE0}"
 	ProjectSection(SolutionItems) = preProject
 		.gitignore = .gitignore
-		.travis.yml = .travis.yml
 		appveyor.yml = appveyor.yml
 		azure-pipelines.yml = azure-pipelines.yml
 		Build.cmd = Build.cmd

ServerHost/ServerHost.csproj

@@ -15,8 +15,6 @@
     <Authors>Jorgen Thelin</Authors>
     <Copyright>Copyright © Jorgen Thelin 2015-2018</Copyright>
     <Description>ServerHost - A .NET Server Hosting utility library, including in-process server host testing.</Description>
-    <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
-    <PackageLicenseFile>LICENSE.txt</PackageLicenseFile>
     <PackageLicenseUrl>https://spdx.org/licenses/Apache-2.0.html</PackageLicenseUrl>
     <PackageProjectUrl>https://github.com/jthelin/ServerHost</PackageProjectUrl>
     <PackageReleaseNotes>Release note are on GitHub https://github.com/jthelin/ServerHost/releases</PackageReleaseNotes>
@@ -60,7 +58,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <None Include="$(SolutionDir)\LICENSE.txt" Pack="true" PackagePath="$(PackageLicenseFile)"/>
+    <None Include="$(SolutionDir)\LICENSE.txt" Pack="true" PackagePath="LICENSE.txt" />
   </ItemGroup>
 
 </Project>