Returns a list of SHA1 hashes used to check server addresses against when the client tries to connect.

*See {@link http://wiki.vg/Mojang_API#Blocked_Servers} for how this list is used.*

@returns {Promise<Array<string>>} resolves to a list of address hashes
function getBlockedServers () {
  return fetch(`${SESSION_API}/blockedservers`, {
    headers: {
      'user-agent': USER_AGENT
    }
  })
    .then(handleErrors)
    .then(res => res.text())
    .then(text => text.split('\n').slice(0, -1))
}