Update doctrine.rst

Hello, I update mysql server version.

Author: abdounikarim

reference/configuration/doctrine.rst

@@ -65,7 +65,7 @@ The following block shows all possible configuration keys:
  charset: UTF8
  logging: '%kernel.debug%'
  platform_service: App\DBAL\MyDatabasePlatformService
- server_version: '5.6'
+ server_version: '5.7'
  mapping_types:
  enum: string
  types:
@@ -99,7 +99,7 @@ The following block shows all possible configuration keys:
  charset="UTF8"
  logging="%kernel.debug%"
  platform-service="App\DBAL\MyDatabasePlatformService"
- server-version="5.6">
+ server-version="5.7">
 
  <doctrine:option key="foo">bar</doctrine:option>
  <doctrine:mapping-type name="enum">string</doctrine:mapping-type>
@@ -121,8 +121,8 @@ The following block shows all possible configuration keys:
 
  Always wrap the server version number with quotes to parse it as a string
  instead of a float number. Otherwise, the floating-point representation
- issues can make your version be considered a different number (e.g. ``5.6``
- will be rounded as ``5.5999999999999996447286321199499070644378662109375``).
+ issues can make your version be considered a different number (e.g. ``5.7``
+ will be rounded as ``5.6999999999999996447286321199499070644378662109375``).
 
  If you don't define this option and you haven't created your database
  yet, you may get ``PDOException`` errors because Doctrine will try to