Fix typo in ns-System.Net.Http.xml (dotnet#5212)

Author: ericmutta

xml/ns-System.Net.Http.xml

@@ -25,7 +25,7 @@
 
 1.  <xref:System.Net.Http.DelegatingHandler> - A class used to plug a handler into a handler chain.
 
-2.  <xref:System.Net.Http.HttpMessageHandler> - A simple to class to derive from that supports the most common requirements for most applications.
+2.  <xref:System.Net.Http.HttpMessageHandler> - A simple class to derive from that supports the most common requirements for most applications.
 
 3.  <xref:System.Net.Http.HttpClientHandler> - A class that operates at the bottom of the handler chain that actually handles the HTTP transport operations.