increase working precision in bernoulli_number_zeta
increase working precision in bernoulli_number_zeta

dsroche/flint2,dsroche/flint2,jpflori/flint2,jpflori/flint2,fredrik-johansson/flint2,wbhart/flint2,fredrik-johansson/flint2,jpflori/flint2,jpflori/flint2,wbhart/flint2,dsroche/flint2,fredrik-johansson/flint2,dsroche/flint2,wbhart/flint2