Bug #1637967: missing //= operator in list.

Doc/ref/ref3.tex

@@ -1999,8 +1999,8 @@ complicated).
 \methodline[numeric object]{__ixor__}{self, other}
 \methodline[numeric object]{__ior__}{self, other}
 These methods are called to implement the augmented arithmetic
-operations (\code{+=}, \code{-=}, \code{*=}, \code{/=}, \code{\%=},
-\code{**=}, \code{<<=}, \code{>>=}, \code{\&=},
+operations (\code{+=}, \code{-=}, \code{*=}, \code{/=}, \code{//=},
+\code{\%=}, \code{**=}, \code{<<=}, \code{>>=}, \code{\&=},
 \code{\textasciicircum=}, \code{|=}).  These methods should attempt to do the
 operation in-place (modifying \var{self}) and return the result (which
 could be, but does not have to be, \var{self}).  If a specific method