use nowdoc instead of heredoc

Author: gharlan

Tests/ConstraintViolationListTest.php

@@ -110,7 +110,7 @@ public function testToString()
             $this->getViolation('Error 5', '', '[baz]'),
         ));
 
-        $expected = <<<EOF
+        $expected = <<<'EOF'
 Root:
     Error 1
 Root.foo.bar:

Tests/ConstraintViolationTest.php

@@ -26,7 +26,7 @@ public function testToStringHandlesArrays()
             null
         );
 
-        $expected = <<<EOF
+        $expected = <<<'EOF'
 Root.property.path:
     Array
 EOF;
@@ -45,7 +45,7 @@ public function testToStringHandlesArrayRoots()
             null
         );
 
-        $expected = <<<EOF
+        $expected = <<<'EOF'
 Array.some_value:
     42 cannot be used here
 EOF;