Update document

Author: aisk

Doc/library/mmap.rst

@@ -233,7 +233,7 @@ To map anonymous memory, -1 should be passed as the fileno along with the length
          Allow specifying *offset* without *size*. Previously, both *offset*
          and *size* parameters were required together. Now *offset* can be
          specified alone, and the flush operation will extend from *offset*
-         to the end of the buffer.
+         to the end of the mmap.
 
 
    .. method:: madvise(option[, start[, length]])