Update reference/constraints/PasswordStrength.rst

Co-authored-by: Matthieu Lempereur <[email protected]>

Author: Spomky

reference/constraints/PasswordStrength.rst

@@ -2,7 +2,7 @@ PasswordStrength
 ================
 
 Validates that the given password has reached the minimum strength required by
-the constraint. The strength is measured using the `zxcvbn-php`_. library.
+the constraint. The strength is measured using the `zxcvbn-php`_ library.
 
 ==========  ===================================================================
 Applies to  :ref:`property or method <validation-property-target>`