Fixing use command issue (#519)

routersploit/core/exploit/utils.py

@@ -84,6 +84,8 @@ def import_exploit(path):
             return getattr(module, "Encoder")
         elif hasattr(module, "Exploit"):
             return getattr(module, "Exploit")
+        else:
+            raise ImportError("No module named '{}'".format(path))
 
     except (ImportError, AttributeError, KeyError) as err:
         raise RoutersploitException(