Update dependency connection_pool to v3

Author: renovate[bot]

Gemfile

@@ -87,7 +87,7 @@ gem 'stringex'
 # gem "image_processing", "~> 1.2"
 
 group :production do
-  gem 'connection_pool', '< 3'
+  gem 'connection_pool', '< 4'
   # Use postgres as the database for Active Record
   gem 'pg'
 end

Gemfile.lock

@@ -122,7 +122,7 @@ GEM
     cgi (0.5.1)
     climate_control (1.2.0)
     concurrent-ruby (1.3.6)
-    connection_pool (2.5.5)
+    connection_pool (3.0.2)
     crack (1.0.1)
       bigdecimal
       rexml
@@ -520,7 +520,7 @@ DEPENDENCIES
   cancancan
   capybara
   climate_control
-  connection_pool (< 3)
+  connection_pool (< 4)
   csv
   debug
   devise