Update copyright dates

[mliu49]

Very straightforward. Just double-check that no unintentional changes were made.

The shebangs were removed from chemkin.pyx and chemkin.pxd because those are now cython files.

[codecov]

Codecov Report

Merging #1539 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1539   +/-   ##
=======================================
  Coverage   42.08%   42.08%           
=======================================
  Files         165      165           
  Lines       27824    27824           
  Branches     5668     5668           
=======================================
  Hits        11711    11711           
  Misses      15328    15328           
  Partials      785      785

Impacted Files	Coverage Δ
rmgpy/data/kinetics/depository.py	61.97% <ø> (ø)	⬆️
rmgpy/molecule/symmetry.py	0% <ø> (ø)	⬆️
rmgpy/data/statmech.py	27.72% <ø> (ø)	⬆️
rmgpy/rmg/pdep.py	16.12% <ø> (ø)	⬆️
rmgpy/restart.py	65.62% <ø> (ø)	⬆️
rmgpy/reduction/output.py	50% <ø> (ø)	⬆️
rmgpy/qm/main.py	72.63% <ø> (ø)	⬆️
rmgpy/molecule/atomtype.py	0% <ø> (ø)	⬆️
rmgpy/reaction.py	0% <ø> (ø)	⬆️
rmgpy/rmg/main.py	22.06% <ø> (ø)	⬆️
... and 84 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f14c7e1...bd08400. Read the comment docs.

[amarkpayne]

Everything looked good, thanks @mliu49!