readme: update line numbers for webhook permission check

In the future, the readme probably should use an alternate means of
indicating why these are necessary, because this link is very fragile.
Either we start referencing a specific code revision (thus potentially
linking to very outdated code, over time), or we stop linking from
documentation into the code like this entirely.

README.md

@@ -74,7 +74,7 @@ external_url = http://your.ip.here:3333/webhook
 
 ### Creating hooks
 
-As an OP+ in a channel, you may type `.gh-hook user/repo`. You will see some informational text on what you need to do to finalize the hook, including a link to click to authorize the creation of the webhook. You will be required to authorize the Github application to read/write your webhooks (see [L167-168](https://github.com/sopel-irc/sopel-github/blob/master/sopel_modules/github/webhook.py#L167-L168)) but this should be the _only_ permissions we need.
+As an OP+ in a channel, you may type `.gh-hook user/repo`. You will see some informational text on what you need to do to finalize the hook, including a link to click to authorize the creation of the webhook. You will be required to authorize the Github application to read/write your webhooks (see [L163-164](https://github.com/sopel-irc/sopel-github/blob/master/sopel_modules/github/webhook.py#L163-L164)) but this should be the _only_ permissions we need.
 
 ```
 <@maxpowa> .gh-hook maxpowa/sopel-github