docs: fix simple typo, vulnerabilty -> vulnerability

There is a small typo in routersploit/modules/exploits/routers/zte/f460_f660_backdoor.py.

Should read `vulnerability` rather than `vulnerabilty`.

routersploit/modules/exploits/routers/zte/f460_f660_backdoor.py

@@ -9,7 +9,7 @@ class Exploit(HTTPClient):
         "description": "Exploits ZTE F460 and F660 backdoor vulnerability that allows "
                        "executing commands on operating system level.",
         "authors": (
-            "Rapid7",  # vulnerabilty discovery
+            "Rapid7",  # vulnerability discovery
             "Marcin Bury <marcin[at]threat9.com>",  # routersploit module
         ),
         "references": (