Update dependency connection_pool to v3

Author: renovate[bot]

Gemfile

@@ -13,7 +13,7 @@ gem "prettyprint", github: "ruby/prettyprint", tag: "v0.2.0"
 
 # locking to connection_pool 2.x until ActiveSupport's memcachestore supports the v3 API
 # see https://github.com/mperham/connection_pool/issues/212
-gem "connection_pool", "< 3"
+gem "connection_pool", "< 4"
 
 gem "pg"
 gem "puma"

Gemfile.lock

@@ -201,7 +201,7 @@ GEM
     cgi (0.4.2)
     coderay (1.1.3)
     concurrent-ruby (1.3.6)
-    connection_pool (2.5.5)
+    connection_pool (3.0.2)
     crass (1.0.6)
     csv (3.3.5)
     cuprite (0.17)
@@ -726,7 +726,7 @@ DEPENDENCIES
   capybara
   civil_service!
   cloudwatch_scheduler!
-  connection_pool (< 3)
+  connection_pool (< 4)
   csv
   cuprite
   dalli