Update Scroll Container in Controller

[jscottsmith]

Updates the controller scroll container in the ParallaxProvider when the element updates. See #56

[codecov-io]

Codecov Report

Merging #57 into master will decrease coverage by 1.09%.
The diff coverage is 58.82%.

@@            Coverage Diff            @@
##           master      #57     +/-   ##
=========================================
- Coverage   91.75%   90.65%   -1.1%     
=========================================
  Files          26       26             
  Lines         279      289     +10     
  Branches       46       47      +1     
=========================================
+ Hits          256      262      +6     
- Misses         18       23      +5     
+ Partials        5        4      -1

Impacted Files	Coverage Δ
src/components/ParallaxProvider.js	100% <100%> (ø)	⬆️
src/classes/ParallaxController.js	74.02% <53.33%> (-7.14%)	⬇️
src/utils/validHTMLElement.js	87.5% <0%> (+37.5%)	⬆️

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