Fix Freebase POST queries
Fix Freebase POST queries

When merging from fsharpx and refactoring to use the Http type, the "X-HTTP-Method-Override" header was missed.
All MQL queries bigger than 1500 characters would fail as they are sent as POST requests
scrwtp/FSharp.Data,AtwooTM/FSharp.Data,olgierdd/FSharp.Data,taylorwood/FSharp.Data,ImaginaryDevelopment/FSharp.Data,NaseUkolyCZ/ApiaryProvider,johansson/FSharp.Data,taylorwood/FSharp.Data,fsprojects/ApiaryProvider,taylorwood/FSharp.Data,olgierdd/FSharp.Data,tpetricek/FSharp.Data,scrwtp/FSharp.Data,olgierdd/FSharp.Data,tpetricek/FSharp.Data,AtwooTM/FSharp.Data,johansson/FSharp.Data,scrwtp/FSharp.Data,ImaginaryDevelopment/FSharp.Data,johansson/FSharp.Data,ImaginaryDevelopment/FSharp.Data,AtwooTM/FSharp.Data,tpetricek/FSharp.Data