test: fix paths to cause exception in ci

Fix paths to cause exception in continuous integration.

#15

Author: josantonius

tests/JsonTest.php

@@ -83,7 +83,7 @@ public function constructorShouldThrowExceptionIfPathIsWrong(): void
     {
         $this->expectException(CreateDirectoryException::class);
 
-        new Json(__DIR__ . '/foo:/filename.json');
+        new Json('/foo:/filename.json');
     }
 
     /**
@@ -94,7 +94,7 @@ public function constructorShouldThrowExceptionIfFilenameIsWrong(): void
     {
         $this->expectException(CreateFileException::class);
 
-        new Json(__DIR__ . '/file:name.json');
+        new Json('/file:name.json');
     }
 
     /**