[Haskell-cafe] network v3.1.2.1

[Kazu Yamamoto (=?iso-2022-jp?B?GyRCOzNLXE9CSScbKEI=?=)]

Hi cafe,

network v3.1.2.1 has been released. This version is bug-fixes only:

* Increasing base lower bound to 4.9.
  [#473](https://github.com/haskell/network/pull/473)
* Suppressing errors from removeFile in UNIX bind.
  [#478](https://github.com/haskell/network/pull/478)
* Restoring UNIX stub functions on Windows.
  [#489](https://github.com/haskell/network/pull/489)

--Kazu