Update ruby

Author: peresvetjke2

.rubocop.yml

@@ -1,5 +1,5 @@
 AllCops:
-  TargetRubyVersion: 2.3
+  TargetRubyVersion: 3.0
   Exclude:
     - 'bin/**/*'
     - 'db/**/*'

.travis.yml

@@ -1,5 +1,5 @@
 language: ruby
 rvm:
-  - 2.3.1
+  - 3.0.6
 services:
   - mongodb

fish0.gemspec

@@ -14,7 +14,7 @@ Gem::Specification.new do |s|
   s.description = 'Plugin for read-only content websites with MongoDB storage.
                    Works perfect with Rambler&Co CQRS projects'
   s.license     = 'MIT'
-  s.required_ruby_version = '~> 2.0'
+  s.required_ruby_version = '~> 3.0'
 
   s.post_install_message = %(
   WARNING starting from 0.1.0 coercion is disabled for Fish0::Model by default