Fix deprecation warning

[nsoranzo]

Fix:

refgenconf/refgenconf.py:13: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3, and in 3.10 it will stop working

[codecov[bot]]

Codecov Report

Merging #116 (e4d2b35) into dev (b77baac) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #116   +/-   ##
=======================================
  Coverage   77.97%   77.98%           
=======================================
  Files          31       31           
  Lines        2579     2580    +1     
=======================================
+ Hits         2011     2012    +1     
  Misses        568      568           

Impacted Files	Coverage Δ
refgenconf/refgenconf.py	67.10% <100.00%> (+0.02%)	:arrow_up:

---

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 b77baac...e4d2b35. Read the comment docs.

[stolarczyk]

thanks @nsoranzo!