Update Directory.Build.props

Analyzers should not be runtime dependencies.

Author: hangy

Directory.Build.props

@@ -29,8 +29,8 @@
 
   <!-- Code Analysis -->
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.6.2" />
-    <PackageReference Include="Roslynator.Analyzers" Version="2.0.0" />
-    <PackageReference Include="Roslynator.CodeFixes" Version="2.0.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.6.2" PrivateAssets="All" />
+    <PackageReference Include="Roslynator.Analyzers" Version="2.0.0" PrivateAssets="All" />
+    <PackageReference Include="Roslynator.CodeFixes" Version="2.0.0" PrivateAssets="All" />
   </ItemGroup>
-</Project>
+</Project>