fixed doc for _fmpz_mat_minpoly methods to reflect return value
fixed doc for _fmpz_mat_minpoly methods to reflect return value

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