fix multiple __init__ calls

[eloyfelix]

Fixes #73

[codecov]

Codecov Report

Merging #74 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
+ Coverage   87.34%   87.37%   +0.03%     
==========================================
  Files           5        5              
  Lines         798      800       +2     
  Branches      118      118              
==========================================
+ Hits          697      699       +2     
  Misses         60       60              
  Partials       41       41

Impacted Files	Coverage Δ
gridData/core.py	94.2% <100%> (+0.04%)	⬆️

---

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 7a76d62...1bf3aec. Read the comment docs.

[orbeckst]

LGTM! (I just added you to the CHANGELOG)

(Apologies for forgetting to review the PR – in the future please feel free to ping me and ask for a review. I won't get mad.)