cannot install for rails 6

[gamesover]

I want to install gem 'timber-rails', but it reports

Fetching gem metadata from https://rubygems.org/.........
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies...
Bundler could not find compatible versions for gem "rails":
  In snapshot (Gemfile.lock):
    rails (= 6.0.0)

  In Gemfile:
    rails (~> 6.0.0)

    timber-rails was resolved to 1.0.1, which depends on
      rails (>= 3.0.0, < 6.0.0)

Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.