Update atomic masses in element.dat
We should use more digits for the masses, as this can be easily obtained from the NIST website
https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=&ascii=ascii
We should use more digits for the masses, as this can be easily obtained from the NIST website
https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=&ascii=ascii