Fix: do not rewrite sw file with history fallback

[mwistrand]

Type: bug

The following has been addressed in the PR:

• There is a related issue
• All code has been formatted with prettier
• Unit or Functional tests are included in the PR

Description:

Update the history fallback rewriter to ignore both files without a referrer (direct access in the browser) and service worker files that are their own referrer.

Resolves #211

[codecov]

Codecov Report

Merging #212 into master will increase coverage by 1.68%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #212      +/-   ##
==========================================
+ Coverage   52.14%   53.83%   +1.68%     
==========================================
  Files          10       10              
  Lines         583      587       +4     
  Branches      142      143       +1     
==========================================
+ Hits          304      316      +12     
+ Misses        279      271       -8

Impacted Files	Coverage Δ
src/main.ts	91.27% <100%> (+4.96%)	⬆️

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