Update README.md: 1 is not a prime
Update README.md: 1 is not a prime

Two small changes were made in this commit:

- Remove the `yield 1;` statement from the body of the `prime`
  function. 1 is not a prime number, and ought not be output
  from this function.

- Change the output array to not contain one. As we're dropping
  a value from the beginning, we need to add a new value at the
  end. I checked carefully that this value is 89, the next
  fibonacci prime. <http://oeis.org/A005478> carries a few more
  terms.

See <http://primes.utm.edu/notes/faq/one.html> for a bunch of
reasons 1 is not a prime.

jussi-kalliokoski/trine,jussi-kalliokoski/trine