Outdated jQuery version 1.12.4

[hiddener]

Describe the bug

Postal uses an outdated jQuery version 1.12.4

To Reproduce

1. Go to jQuery Detection Tool
2. Enter a postal server URL
3. See Version detected: 1.12.4

Expected behaviour

Postal must use a more recent jQuery version. Is this as simple as editing the line below to require jquery3?

postal/app/assets/javascripts/application/application.coffee

Line 1 in d038eaa

#= require jquery

[willpower232]

I presume the jquery-rails gem will need updating. Feel free to give it a go and make a PR