Merge pull request #33875 from yahonda/drop_mysql_51_support

Bump MySQL version requirement to 5.5.8 in the template files

[ci skip]

railties/lib/rails/generators/rails/app/templates/config/databases/jdbcmysql.yml.tt

-# MySQL. Versions 5.1.10 and up are supported.
+# MySQL. Versions 5.5.8 and up are supported.
 #
 # Install the MySQL driver:
 #   gem install activerecord-jdbcmysql-adapter

railties/lib/rails/generators/rails/app/templates/config/databases/mysql.yml.tt

-# MySQL. Versions 5.1.10 and up are supported.
+# MySQL. Versions 5.5.8 and up are supported.
 #
 # Install the MySQL driver
 #   gem install mysql2