XML is not well-formed (#740)

XML is not well-formed due to the duplicated closing tag

SHFB/Source/PresentationStyles/OpenXml/Content/ReferenceContent.xml

@@ -274,7 +274,7 @@
   <!-- Variance boilerplate text -->
   <item id="text_covariant">This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. </item>
   <item id="text_contravariant">This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. </item>
-  <item id="text_variance">For more information about covariance and contravariance, see <a href="https://docs.microsoft.com/dotnet/visual-basic/programming-guide/concepts/covariance-contravariance/index">Covariance and Contravariance (Visual Basic)</a> and <a href="https://docs.microsoft.com/dotnet/csharp/programming-guide/concepts/covariance-contravariance/index">Covariance and Contravariance (C#)</a>.</a>.</item>
+  <item id="text_variance">For more information about covariance and contravariance, see <a href="https://docs.microsoft.com/dotnet/visual-basic/programming-guide/concepts/covariance-contravariance/index">Covariance and Contravariance (Visual Basic)</a> and <a href="https://docs.microsoft.com/dotnet/csharp/programming-guide/concepts/covariance-contravariance/index">Covariance and Contravariance (C#)</a>.</item>
 
   <!-- Non CLS Compliant boilerplate text-->
   <item id="boilerplate_NotClsCompliant">This API is not CLS-compliant.</item>