Remove Ruby version lock from Gemfile

Gemfile

@@ -1,8 +1,6 @@
 source 'https://rubygems.org'
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
-ruby '2.6.1'
-
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem 'rails', '~> 6.0.3', '>= 6.0.3.4'
 # Use sqlite3 as the database for Active Record