Add NODE_ENV=development to test script to see React errors

[kuychaco]

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Description of the Change

This PR sets our test script to run with NODE_ENV=development. Doing so helped us catch/debug a React issue as described in f60d186

Rationale: React runs fewer checks in production mode for efficiency. For example, in development mode it checks that props have not been mutated but in production mode it seems that it does not. We had an issue where tests were failing on CI due to mutated props but not locally until we set the NODE_ENV to be development. Presumably our CI is running with development mode by default. Let's just have this always be the case to err on the side of catching more errors locally.

Screenshot/Gif

N/A

Alternate Designs

N/A

Benefits

Catch bugs more easily / faster!

Possible Drawbacks

None.

Applicable Issues

See f60d186

Metrics

N/A

Tests

N/A

Documentation

N/A

Release Notes

Run tests with NODE_ENV=development to catch dev-mode React errors locally

User Experience Research (Optional)

N/A

[codecov]

Codecov Report

Merging #2113 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2113      +/-   ##
==========================================
+ Coverage   92.65%   92.66%   +<.01%     
==========================================
  Files         207      207              
  Lines       12045    12045              
  Branches     1764     1764              
==========================================
+ Hits        11160    11161       +1     
+ Misses        885      884       -1

Impacted Files	Coverage Δ
lib/atom/gutter.js	92.3% <0%> (+2.56%)	⬆️

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[smashwilson]

👍 Thanks!