fix exception types for span (#2653)

Author: mairaw

xml/System/Span`1.xml

@@ -121,7 +121,7 @@ If `array` is `null`, this constructor returns a `null` `Span<T>`.
 
       ]]></format>
         </remarks>
-        <exception cref="T:System.TypeMismatchException">
+        <exception cref="T:System.ArrayTypeMismatchException">
           <paramref name="T" /> is a reference type, and <paramref name="array" /> is not an array of type <paramref name="T" />.</exception>
       </Docs>
     </Member>
@@ -212,7 +212,7 @@ If `array` is `null`, this constructor returns a `null` `Span<T>`.
 
 <paramref name="start" /> and <paramref name="length" /> exceeds the number of elements in the array.
         </exception>
-        <exception cref="T:System.TypeMismatchException">
+        <exception cref="T:System.ArrayTypeMismatchException">
           <paramref name="T" /> is a reference type, and <paramref name="array" /> is not an array of type <paramref name="T" />.</exception>
       </Docs>
     </Member>
@@ -1106,4 +1106,4 @@ If `destination` is shorter than the source <xref:System.Span%601>, this method
       </Docs>
     </Member>
   </Members>
-</Type>
+</Type>