Indicate which class/method was actually using.

Knowing the method is defined in a trait is not as helpful as knowing
which class has the method called on it.

src/Core/InstanceConfigTrait.php

@@ -176,7 +176,7 @@ trait InstanceConfigTrait
     public function config($key = null, $value = null, $merge = true)
     {
         deprecationWarning(
-            'InstanceConfigTrait::config() is deprecated. ' .
+            get_called_class() . '::config() is deprecated. ' .
             'Use setConfig()/getConfig() instead.'
         );
 

src/Core/StaticConfigTrait.php

@@ -164,7 +164,7 @@ trait StaticConfigTrait
     public static function config($key, $config = null)
     {
         deprecationWarning(
-            'StaticConfigTrait::config() is deprecated. ' .
+            get_called_class() . '::config() is deprecated. ' .
             'Use setConfig()/getConfig() instead.'
         );