[MoarVM Bump] Brings 8 commits

MoarVM bump brought: MoarVM/MoarVM@2019.07.1-249-g01f85c8bf...2019.07.1-257-g39f577438
39f577438 Merge pull request #1166 from Kaiepi/ipv6-unsupported
379ec77a1 Ensure UDP sockets actually get bound when binding them
d9a067d46 Never call freeaddrinfo more than once, always hold on to socket errors
2f4798b85 Actually fix GC in async sockets
3fa99b4dc Fix some memory issues and race conditions with async sockets
2b835211d Actually make async sockets work again
5bf9e00c4 Try using all resolved addresses before throwing
5533a7873 Use more appropriate flags in MVM_io_resolve_host_name

tools/templates/MOAR_REVISION

@@ -1 +1 @@
-2019.07.1-249-g01f85c8bf
+2019.07.1-257-g39f577438