Convert pubchem_mass to float

[dianacarvalho1]

When trying to call pubchem_metadata_lookup(), the following error is being raised:

            pubchem_mass = results_pubchem[0].exact_mass
>           match_mass = (np.abs(pubchem_mass - parent_mass) <= mass_tolerance)
E           TypeError: unsupported operand type(s) for -: 'str' and 'float'

/Users/user/anaconda3/envs/omigami/lib/python3.7/site-packages/matchmsextras/pubchem_lookup.py:328: TypeError

This is happening because results_pubchem[0].exact_mass is a string and not a float.

[florian-huber]

Thanks a lot for the PR. Fix looks good to me!

[florian-huber]

@dianacarvalho1 I merged your fix and will do a small new release (0.2.3).
Please feel free to add your name/orcid to the CITATION.cff file!