Don't run through fire about mineflayer-navigate

[andrewrk]

I think this list should live in navigate, not mineflayer

[andrewrk]

Proposed API:

bot.navigate.blocksToAvoid = {
  51: true, // fire
  59: true, // wheat
  ...
}

And it should come with sensible defaults.

And then in the code, isSafe will check this property and return false if it is a block to avoid.

[thejoshwolfe]

sounds good