make documented file() kw names and actual ones agree (closes #15572)

Patch by Daniel Ellis.
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index dc8ee9a..30ac614 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -451,7 +451,7 @@
       used reliably to modify a function's locals.
 
 
-.. function:: file(filename[, mode[, bufsize]])
+.. function:: file(name[, mode[, buffering]])
 
    Constructor function for the :class:`file` type, described further in section
    :ref:`bltin-file-objects`.  The constructor's arguments are the same as those