Update to use minecraft-data for toMajor()

[deathcap]

lib/loader.js currently gets the major version from the release version by splitting the string:

function toMajor(mcVersion)
{
  var parts=mcVersion.split(".");
  if(parts.size<=1)
    return null;
  mcVersion=parts.slice(0,2).join(".");
  return mcVersion;
}

This works for full releases, but snapshot versions can be said to resemble certain "major" versions, which won't be parsed here. Instead this mapping can be looked up using minecraft-data, after:

PrismarineJS/minecraft-data#92 Add protocol version data

protocolVersions.json array, "majorVersion" key

(may also want to keep toMajor() as a fallback)

[rom1504]

well I did half of that but forgot the other half (PrismarineJS/node-minecraft-protocol#330 (comment)).
Will finish this later.