style: correct code style violations

Author: DannyvdSluijs

src/JsonSchema/Constraints/Drafts/Draft06/Draft06Constraint.php

@@ -14,7 +14,6 @@ class Draft06Constraint extends Constraint
 {
     public function __construct(?\JsonSchema\Constraints\Factory $factory = null)
     {
-
         parent::__construct(new Factory(
             $factory ? $factory->getSchemaStorage() : new SchemaStorage(),
             $factory ? $factory->getUriRetriever() : new UriRetriever(),

src/JsonSchema/Constraints/Drafts/Draft06/MinimumConstraint.php

@@ -25,7 +25,7 @@ public function check(&$value, $schema = null, ?JsonPointer $path = null, $i = n
             return;
         }
 
-        if (! is_numeric($value)) {
+        if (!is_numeric($value)) {
             return;
         }
 

src/JsonSchema/Constraints/Drafts/Draft06/RefConstraint.php

@@ -4,7 +4,6 @@
 
 namespace JsonSchema\Constraints\Drafts\Draft06;
 
-use JsonSchema\ConstraintError;
 use JsonSchema\Constraints\ConstraintInterface;
 use JsonSchema\Entity\ErrorBagProxy;
 use JsonSchema\Entity\JsonPointer;