Upgrade to Stackage nightly 2018-06-01

[tfausak]

Sadly the build fails:

336    C:\Users\appveyor\AppData\Local\Temp\1\stack2172\network-2.6.3.5\Network\Socket\Types.hsc:764:16: error:
337        parse error on input `CALLCONV'
338        |
339    764 | foreign import CALLCONV unsafe "ntohs" ntohs :: Word16 -> Word16
340        |     

Related issues:

• GHC 8.4 syntax error (on Windows specifically; Linux and OS X are fine) haskell/network#313
• Network as a dependency fails to build with GHC 8.4.1 commercialhaskell/stack#3944

[tfausak]

This worked fine locally (Windows) and on Linux and on OS X. I think I'll wait for LTS 12 to roll around before changing the resolver.