Adding Support for Jest

[cfcomputing]

I ran into a similar issue when using Jest as was report in: https://github.com/dwyl/decache/issues/27

I changed it locally while just trying to debug and figure out what was going on and as such I figured you may want to have support added to make it seamless for those of us using Jest. If not no worries at all just figured I would send it over since I already had the code written.

[codecov[bot]]

Codecov Report

Merging #37 into master will decrease coverage by 2.04%. The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
- Coverage     100%   97.95%   -2.05%     
==========================================
  Files           4        4              
  Lines          47       49       +2     
==========================================
+ Hits           47       48       +1     
- Misses          0        1       +1

Impacted Files	Coverage Δ
decache.js	97.05% <66.66%> (-2.95%)	:arrow_down:

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