Fix typo in Range.xml

One occurrence of "does't".

Author: stevemonaco

xml/System/Range.xml

@@ -353,7 +353,7 @@ int[] subArray2 = someArray[1..^0];              // { 2, 3, 4, 5 }
 
 ## Remarks
 
-For performance reasons, this method does't validate `length` to ensure that it is not negative. It does ensure that `length` is within the current `Range` instance.
+For performance reasons, this method doesn't validate `length` to ensure that it is not negative. It does ensure that `length` is within the current `Range` instance.
 
           ]]></format>
         </remarks>