Use `` in KeyIsNotDefined message

Author: vudaltsov

src/KeyIsNotDefined.php

@@ -13,6 +13,6 @@ final class KeyIsNotDefined extends \RuntimeException
 {
     public function __construct(Key $key)
     {
-        parent::__construct(\sprintf('Key %s is not defined in the TypedMap', format($key)));
+        parent::__construct(\sprintf('Key `%s` is not defined in the TypedMap', format($key)));
     }
 }

tests/KeyIsNotDefinedTest.php

@@ -14,6 +14,6 @@ public function testMessage(): void
     {
         $exception = new KeyIsNotDefined(Keys::A);
 
-        self::assertSame('Key Typhoon\TypedMap\Keys::A is not defined in the TypedMap', $exception->getMessage());
+        self::assertSame('Key `Typhoon\TypedMap\Keys::A` is not defined in the TypedMap', $exception->getMessage());
     }
 }