Cannot update momentjs-rails due to dependency

[stuartluscombe]

I have an error in my application which states

 Uncaught Error: Tempus Dominus Bootstrap4's requires at least moment.js v2.17.0 but less than v3.0.0

However, when trying to update momentjs-rails to a version >= 2.17.0 I then get an error stating

Bundler could not find compatible versions for gem "momentjs-rails":
  In Gemfile:
    momentjs-rails (>= 2.17.0, < 3.0.0)

    moment_timezone-rails was resolved to 0.5.25, which depends on
      momentjs-rails (~> 2.15.1)

Could the gemspec please be updated to allow a later version?