Fixed bug with content not being updated

[Blackbaud-SteveBrush]

• Content would only get updated by the last plugin in the array
• Added tests

[codecov-io]

Codecov Report

Merging #124 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #124   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          32     32           
  Lines         679    678    -1     
  Branches       83     83           
=====================================
- Hits          679    678    -1

Flag	Coverage Δ
#builder	100% <100%> (ø)	⬆️
#runtime	100% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
runtime/config.ts	100% <ø> (ø)	⬆️
loader/sky-processor/index.js	100% <100%> (ø)	⬆️

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