Fix sw.js overwrite

[luisjoserivera]

• Workbox options should be under pwa.
• Both scripts (OneSignalSDKWorker.js and OneSignalSDKUpdaterWorker.js) should be modified to import sw.js in accordance with OneSignal documentation https://documentation.onesignal.com/docs/onesignal-service-worker-faq#integrating-multiple-service-workers

Fixes #1

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.00%. Comparing base (885888d) to head (653df8f).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/module.js	66.66%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
- Coverage   75.00%   70.00%   -5.00%     
==========================================
  Files           2        2              
  Lines          48       50       +2     
  Branches        9       11       +2     
==========================================
- Hits           36       35       -1     
- Misses         12       15       +3     

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