[PRISM] Enable Socket.gethostbyaddr spec

spec/prism.mspec

@@ -6,7 +6,3 @@ MSpec.register(:exclude, "TracePoint#path equals \"(eval at __FILE__:__LINE__)\"
 
 # We need to respect the eval coverage setting.
 MSpec.register(:exclude, "Coverage.result returns the correct results when eval coverage is disabled")
-
-# I'm not sure why this is failing, it passes on my machine. Leaving this off
-# until we can investigate it more.
-MSpec.register(:exclude, "Socket.gethostbyaddr using an IPv6 address with an explicit address family raises SocketError when the address is not supported by the family")