Add docs on how to turn off SSL verification on GH oauth

In gitlab-ee!323 we added support to disable SSL verification because attempting to import projects from a self-signed GH Enterprise instance will fail with an SSL error.

doc/integration/github.md

@@ -125,7 +125,7 @@ For omnibus package:
       "app_id" => "YOUR_APP_ID",
       "app_secret" => "YOUR_APP_SECRET",
       "url" => "https://github.com/",
-      "verify" => false,
+      "verify_ssl" => false,
       "args" => { "scope" => "user:email" }
     }
   ]
@@ -137,7 +137,7 @@ For installation from source:
   - { name: 'github', app_id: 'YOUR_APP_ID',
     app_secret: 'YOUR_APP_SECRET',
     url: "https://github.example.com/",
-    verify: false,
+    verify_ssl: false,
     args: { scope: 'user:email' } }
 ```