Drop MySQL 5.1 support

* MySQL 5.1 does not support `utf8mb4` character set

* MySQL 5.1 had been already EOLed on Dec 2013
https://www.mysql.com/support/eol-notice.html

> Per Oracle's Lifetime Support policy, as of December 31, 2013, MySQL 5.1
> is covered under Oracle Sustaining Support.

* MySQL 5.5.8 is the first General Availability of MySQL 5.5

https://dev.mysql.com/doc/relnotes/mysql/5.5/en/news-5-5-8.html

2 files changed, 6 insertions, 2 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 0bb5dfe313..942a6ca282 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Bump minimum MySQL version to 5.5.8.
+
+    *Yasuo Honda*
+
 *   Use MySQL utf8mb4 character set by default.
 
     `utf8mb4` character set with 4-Byte encoding supports supplementary characters including emoji.
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 982a38d6e1..5d4fc8324f 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -53,8 +53,8 @@ module ActiveRecord
 
         @statements = StatementPool.new(self.class.type_cast_config_to_integer(config[:statement_limit]))
 
-        if version < "5.1.10"
-          raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.1.10."
+        if version < "5.5.8"
+          raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.5.8."
         end
       end