[Haskell-cafe] network v3.1.2.1

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