renamed exception to be more consistent with original PHP one

src/exceptions.php

 <?php declare(strict_types=1);
 namespace Grifart\AssertFunction;
 
-use Throwable;
-
-
-
-final class AssertFunctionError extends \AssertionError {
+final class FunctionAssertionError extends \AssertionError {
 
 	const PATH_DEPTH = 2;
 
@@ -53,5 +49,3 @@ final class AssertFunctionError extends \AssertionError {
 		return implode('/', $pathParts); // normalized shortened readable path
 	}
 };
-
-abstract class RuntimeException extends \RuntimeException {};