Configure Uglifier gem to minify js

[Tlazypanda]

Fixes #7887
Uglifier gem is configured to minify javascript files.

Tested in development by setting the asset compilation as true(setting the config.assets.debug to false and config.assets.compile to true in development.rb) and checking the asset files.

Make sure these boxes are checked before your pull request (PR) is ready to be reviewed and merged. Thanks!

• PR is descriptively titled 📑 and links the original issue above 🔗
• tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR -- or run tests locally with rake test
• code is in uniquely-named feature branch and has no merge conflicts 📁
• screenshots/GIFs are attached 📎 in case of UI updation
• ask @publiclab/reviewers for help, in a comment below

Thanks!

[codecov]

Codecov Report

Merging #7937 into master will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #7937      +/-   ##
==========================================
+ Coverage   82.04%   82.16%   +0.12%     
==========================================
  Files          97       97              
  Lines        5642     5642              
==========================================
+ Hits         4629     4636       +7     
+ Misses       1013     1006       -7     

Impacted Files	Coverage Δ
app/controllers/stats_controller.rb	73.33% <100.00%> (ø)
app/api/srch/search.rb	70.06% <0.00%> (+3.82%)	⬆️
app/services/execute_search.rb	94.44% <0.00%> (+5.55%)	⬆️

[cesswairimu]

travis has been running forever on this 🤔 @Tlazypanda try closing the PR and reopening

[Tlazypanda]

@cesswairimu Travis passed yay!! 😄

[Tlazypanda]

@jywarren @cesswairimu @emilyashley @SidharthBansal @VladimirMikulic can you kindly review? Thanks ✌️

[Uzay-G]

This looks good, the harmony mode will allow us to use ES6 so that is nice.

[Tlazypanda]

@Uzay-G Thanks a lot for the review 😄

[jywarren]

Love this! Merging!!!