Add backticks to table name

In postgres the table user has a reserved meaning, so we need to add backticks to the table name so that doctrine is able to add quotes to the table name. See #77 and doctrine/dbal#572 for some related issues

config/xml/zfcuserdoctrineorm/ZfcUserDoctrineORM.Entity.User.dcm.xml

@@ -4,7 +4,7 @@
                   xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
                   http://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
 
-    <entity name="ZfcUserDoctrineORM\Entity\User" table="user">
+    <entity name="ZfcUserDoctrineORM\Entity\User" table="`user`">
 
     </entity>