Add Utils method to check for integer

[yuyokk]

Hi guys,

I faced the issue with Number.isInteger on IE11 and see that this method is not supported there.
There is a Polyfill available on MDN
so I've added an utils method for checking isInteger.

Please let me know if this makes sense.
Thanks

[codecov-io]

Codecov Report

Merging #185 into master will decrease coverage by 0.06%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master     #185      +/-   ##
==========================================
- Coverage   90.89%   90.83%   -0.07%     
==========================================
  Files          53       53              
  Lines        2493     2498       +5     
  Branches      504      506       +2     
==========================================
+ Hits         2266     2269       +3     
- Misses        217      219       +2     
  Partials       10       10

Impacted Files	Coverage Δ
packages/aws-amplify/src/Cache/StorageCache.ts	78.72% <100%> (ø)	⬆️
packages/aws-amplify/src/Cache/Utils/CacheUtils.ts	81.81% <60%> (-6.42%)	⬇️

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[powerful23]

👍 @yuyokk Great!

[github-actions]

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