Update pg gem required version to 1.1

This is required for #39063 to use `PG::TextDecoder::Numeric`.

Ref https://github.com/ged/ruby-pg/pull/25.

The pg gem 1.1.0 was released at August 24, 2018, so I think it is good
timing to bump the required version for improving and cleaning up the
code base.

https://rubygems.org/gems/pg/versions

Gemfile

@@ -127,7 +127,7 @@ platforms :ruby, :mswin, :mswin64, :mingw, :x64_mingw do
   gem "sqlite3", "~> 1.4"
 
   group :db do
-    gem "pg", ">= 0.18.0"
+    gem "pg", "~> 1.1"
     gem "mysql2", "~> 0.5"
   end
 end

Gemfile.lock

@@ -569,7 +569,7 @@ DEPENDENCIES
   minitest-retry
   mysql2 (~> 0.5)
   nokogiri (>= 1.8.1)
-  pg (>= 0.18.0)
+  pg (~> 1.1)
   psych (~> 3.0)
   puma
   que

actioncable/lib/action_cable/subscription_adapter/postgresql.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-gem "pg", ">= 0.18", "< 2.0"
+gem "pg", "~> 1.1"
 require "pg"
 require "thread"
 require "digest/sha1"

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -1,17 +1,8 @@
 # frozen_string_literal: true
 
-# Make sure we're using pg high enough for type casts and Ruby 2.2+ compatibility
-gem "pg", ">= 0.18", "< 2.0"
+gem "pg", "~> 1.1"
 require "pg"
 
-# Use async_exec instead of exec_params on pg versions before 1.1
-class ::PG::Connection # :nodoc:
-  unless self.public_method_defined?(:async_exec_params)
-    remove_method :exec_params
-    alias exec_params async_exec
-  end
-end
-
 require "active_support/core_ext/object/try"
 require "active_record/connection_adapters/abstract_adapter"
 require "active_record/connection_adapters/statement_pool"
@@ -905,14 +896,10 @@ module ActiveRecord
             "float4" => PG::TextDecoder::Float,
             "float8" => PG::TextDecoder::Float,
             "bool" => PG::TextDecoder::Boolean,
+            "timestamp" => PG::TextDecoder::TimestampUtc,
+            "timestamptz" => PG::TextDecoder::TimestampWithTimeZone,
           }
 
-          if defined?(PG::TextDecoder::TimestampUtc)
-            # Use native PG encoders available since pg-1.1
-            coders_by_name["timestamp"] = PG::TextDecoder::TimestampUtc
-            coders_by_name["timestamptz"] = PG::TextDecoder::TimestampWithTimeZone
-          end
-
           known_coder_types = coders_by_name.keys.map { |n| quote(n) }
           query = <<~SQL % known_coder_types.join(", ")
             SELECT t.oid, t.typname

railties/lib/rails/generators/database.rb

@@ -14,7 +14,7 @@ module Rails
       def gem_for_database(database = options[:database])
         case database
         when "mysql"          then ["mysql2", ["~> 0.5"]]
-        when "postgresql"     then ["pg", [">= 0.18", "< 2.0"]]
+        when "postgresql"     then ["pg", ["~> 1.1"]]
         when "sqlite3"        then ["sqlite3", ["~> 1.4"]]
         when "oracle"         then ["activerecord-oracle_enhanced-adapter", nil]
         when "sqlserver"      then ["activerecord-sqlserver-adapter", nil]

railties/test/generators/app_generator_test.rb

@@ -547,7 +547,7 @@ class AppGeneratorTest < Rails::Generators::TestCase
     if defined?(JRUBY_VERSION)
       assert_gem "activerecord-jdbcpostgresql-adapter"
     else
-      assert_gem "pg", "'>= 0.18', '< 2.0'"
+      assert_gem "pg", "'~> 1.1'"
     end
   end
 

railties/test/generators/db_system_change_generator_test.rb

@@ -40,7 +40,7 @@ module Rails
 
             assert_file("Gemfile") do |content|
               assert_match "# Use pg as the database for Active Record", content
-              assert_match "gem 'pg', '>= 0.18', '< 2.0'", content
+              assert_match "gem 'pg', '~> 1.1'", content
             end
           end