Fix molecular formula regex

[chasemc]

Fixes issue where formula with atom counts containing a zero result in parse error

for example:

Works:

https://massql.gnps2.org/parse?query=QUERY%20MS2DATA%20WHERE%20MS1MZ=formula(C1)

Doesn't work:

https://massql.gnps2.org/parse?query=QUERY%20MS2DATA%20WHERE%20MS1MZ=formula(C10)