Fixing calculation of GC content to be correct.

[jonn-smith]

Fixes #4600

[LeeTL1220]

@jonn-smith feel free to merge...

[codecov-io]

Codecov Report

Merging #4608 into master will increase coverage by 0.093%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##              master     #4608       +/-   ##
===============================================
+ Coverage     79.853%   79.946%   +0.093%     
- Complexity     17052     17237      +185     
===============================================
  Files           1067      1067               
  Lines          62029     62497      +468     
  Branches       10037     10157      +120     
===============================================
+ Hits           49532     49964      +432     
- Misses          8585      8597       +12     
- Partials        3912      3936       +24

Impacted Files	Coverage Δ	Complexity Δ
...dataSources/gencode/GencodeFuncotationFactory.java	81.34% <100%> (+0.615%)	144 <0> (+4)	⬆️
...ataSources/xsv/SimpleKeyXsvFuncotationFactory.java	88.722% <0%> (+1.222%)	47% <0%> (+21%)	⬆️
...org/broadinstitute/hellbender/engine/GATKTool.java	92.705% <0%> (+1.401%)	186% <0%> (+93%)	⬆️
...tools/funcotator/DataSourceFuncotationFactory.java	91.837% <0%> (+1.837%)	22% <0%> (+5%)	⬆️
...ools/funcotator/FuncotatorArgumentDefinitions.java	87.719% <0%> (+2.613%)	1% <0%> (ø)	⬇️
...r/dataSources/cosmic/CosmicFuncotationFactory.java	85.294% <0%> (+4.241%)	33% <0%> (+12%)	⬆️
.../tools/funcotator/dataSources/DataSourceUtils.java	72.348% <0%> (+4.301%)	33% <0%> (+7%)	⬆️
...ataSources/xsv/LocatableXsvFuncotationFactory.java	88.722% <0%> (+4.851%)	39% <0%> (+13%)	⬆️
...titute/hellbender/tools/funcotator/Funcotator.java	81.221% <0%> (+4.869%)	49% <0%> (+19%)	⬆️
... and 2 more