Fix type errors

[mhidas]

Fixes#117

[codecov]

Codecov Report

Merging #151 (7cdd401) into master (f4dca31) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #151 +/- ##
==========================================
+ Coverage 70.44% 70.46% +0.02% 
==========================================
Files 12 12 Lines 1130 1131 +1 Branches 151 152 +1 ==========================================
+ Hits 796 797 +1 
Misses 317 317 Partials 17 17 

Impacted Files	Coverage Δ
...tools/timeseries_products/aggregated_timeseries.py	95.15% <100.00%> (-0.15%)	⬇️
aodntools/timeseries_products/common.py	88.73% <100.00%> (+2.29%)	⬆️
aodntools/timeseries_products/hourly_timeseries.py	98.17% <100.00%> (-0.05%)	⬇️

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[mhidas]

@evacougnon@leonardolaiolo I've tagged you both as reviewers, but only really need one. To be discussed with @ggalibert who will have time for this next iteration (or later...)