feat: add support for multiple retries

[ayushya]

Summary
I have added support for multiple retries via a config parameter maxRetries whose default value is 1.

This PR has the following changes:

1. Added support for multiple retries via maxRetries option.
2. Default value of maxRetries is 1.
3. Since each of the retry attempts should have a unique URL, the cacheBusting URL is changed on each retry attempt. This is done by calling the functiongetCacheBustString every time.
4. Have updated the README with the instructions to use this option.

Update

1. Have updated the e2e to testing suite to verify the behavior with maxRetries.
2. We also append &retryAttempt=attemptValue in the query string to track retryAttempt.

This closes #4

[codecov-io]

Codecov Report

Merging #5 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #5   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          13     16    +3     
  Branches        2      3    +1     
=====================================
+ Hits           13     16    +3

Impacted Files	Coverage Δ
src/index.js	100% <100%> (ø)	⬆️

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[ayushya]

@mattlewis92 Did you get a chance to review this PR?

[ayushya]

@b1rdex I have updated the PR.
Can you re-review this?

[mattlewis92]

This is great work @ayushya and thanks a lot to @b1rdex for reviewing as well. Really appreciate it! ❤️

[mattlewis92]

Released as 1.2.0 🎉

[ayushya]

This is great work @ayushya and thanks a lot to @b1rdex for reviewing as well. Really appreciate it! ❤️

It was fun to work on this.