Update CacheControlHeaderValue.xml (#2006)

Added a "not" in the description of the NoCache property.

Author: boskjoett

xml/System.Net.Http.Headers/CacheControlHeaderValue.xml

@@ -378,7 +378,7 @@
       <Docs>
         <summary>Whether an HTTP client is willing to accept a cached response.</summary>
         <value>
-          <see langword="true" /> if the HTTP client is willing to accept a cached response; otherwise, <see langword="false" />.</value>
+          <see langword="true" /> if the HTTP client is not willing to accept a cached response; otherwise, <see langword="false" />.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[  
   
@@ -861,4 +861,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
+</Type>