Fix Directory.Build.props casing and latest SDK

Author: Nick Craver

StackExchange.Utils.sln

@@ -5,14 +5,14 @@ VisualStudioVersion = 15.0.27705.2000
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{F0CFAC4D-516B-45DC-8F66-D58E3B1C04E1}"
 	ProjectSection(SolutionItems) = preProject
-		src\Directory.build.props = src\Directory.build.props
+		src\Directory.Build.props = src\Directory.Build.props
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "StackExchange.Utils.Http", "src\StackExchange.Utils.Http\StackExchange.Utils.Http.csproj", "{168B503A-428F-499D-99A7-8EFC47A5FEDF}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{9133A680-3A8F-4662-AA58-B59BBDD0A60E}"
 	ProjectSection(SolutionItems) = preProject
-		tests\Directory.build.props = tests\Directory.build.props
+		tests\Directory.Build.props = tests\Directory.Build.props
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "StackExchange.Utils.Tests", "tests\StackExchange.Utils.Tests\StackExchange.Utils.Tests.csproj", "{33716E0F-FE40-4A7A-9F58-1026EF7EBCD2}"

src/Directory.build.props renamed to src/Directory.Build.props

@@ -9,7 +9,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.3.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.3.0" />
     <PackageReference Include="xunit" Version="$(xUnitVersion)" />
     <PackageReference Include="xunit.runner.visualstudio" Version="$(xUnitVersion)" />
   </ItemGroup>