Tweaked the explanation of UniqueEntity constraint

Author: javiereguiluz

reference/constraints/UniqueEntity.rst

@@ -28,8 +28,7 @@ Basic Usage
 
 Suppose you have an AppBundle bundle with a ``User`` entity that has
 an ``email`` field. You can use the ``UniqueEntity`` constraint to guarantee
-that the ``email`` field remains unique between all of the constraints in
-your user table:
+that the ``email`` field remains unique between all of the rows in your user table:
 
 .. configuration-block::