Replace ./ with . so projects build correctly based on docs

Author: sander1095

aspnetcore/fundamentals/openapi/aspnetcore-openapi.md

@@ -160,7 +160,7 @@ By default, the generated OpenAPI document will be emitted to the application's
 
 ```xml
 <PropertyGroup>
-  <OpenApiDocumentsDirectory>./</OpenApiDocumentsDirectory>
+  <OpenApiDocumentsDirectory>.</OpenApiDocumentsDirectory>
 </PropertyGroup>
 ```