fix the preload headers for crossorigin requests

[vigneshshanmugam]

• To fix the double requests when things are changed dynamically though requirejs hooks

[codecov-io]

Codecov Report

Merging #130 into master will increase coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #130      +/-   ##
==========================================
+ Coverage   92.24%   92.32%   +0.07%     
==========================================
  Files          13       13              
  Lines         503      508       +5     
  Branches       89       90       +1     
==========================================
+ Hits          464      469       +5     
  Misses         39       39

Impacted Files	Coverage Δ
lib/request-handler.js	97% <100%> (+0.15%)	✅

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