Between major versions 2 and 3, we hit a bug. It's fixed in version 3,
however, the explicit 2.x requirement of `~> '2.0'` will prevent people
from getting the fix with `bundle update` and they would have to
explicitly set the constraint to `~> '3.0'`.

For more information see: rails/web-console#178.

I propose we drop the explicit version constraints in the Gemfile. Web
Console has been relatively stable for the past couple of years, and I
don't anticipate any major alterations, like we saw between major
versions 1 and 2.