🐛 fix error message if data or output directories do not exist

config.py.example

@@ -17,6 +17,6 @@ class Config:
     DEBUG      = False
 
     if not os.path.exists(DATA_DIR):
-        raise "DATA_DIR does not exist"
+        raise RuntimeError("DATA_DIR does not exist")
     if not os.path.exists(OUT_DIR):
-        raise "OUT_DIR does not exist"
+        raise RuntimeError("OUT_DIR does not exist")