minor grammar update (home-assistant#3702)

Guyanthalas · fabaff · commit c51c5b4234f8 · 2017-10-21T21:23:23.000+02:00
diff --git a/source/_docs/configuration/secrets.markdown b/source/_docs/configuration/secrets.markdown
@@ -23,7 +23,7 @@ http:
   api_password: YOUR_PASSWORD
 ```
 
-Those entries need to be replaced with `!secret` and a identifier.
+Those entries need to be replaced with `!secret` and an identifier.
 
 ```yaml
 http:
