Update Capistrano lock version in config/deploy.rb (#4352)

Deployment with Capistrano was failing due to a mismatch between the loaded
version of Capistrano and the one specified in the deployment
configuration. Bumping the version in config/deploy.rb fixes this issue.

config/deploy.rb

 # frozen_string_literal: true
 
-lock '3.8.1'
+lock '3.8.2'
 
 set :repo_url, ENV.fetch('REPO', 'https://github.com/tootsuite/mastodon.git')
 set :branch, ENV.fetch('BRANCH', 'master')