Google.Colon ignores accept.txt

`Search: Google` gets flagged, even if you add Google to `accept.txt`. Can be fixed by adding the following to `Colon.yml`

```diff
extends: existence
message: "'%s' should be in lowercase."
link: "https://developers.google.com/style/colons"
nonword: true
level: warning
scope: sentence
tokens:
  - ':\s[A-Z]'
+exceptions:
+  -
```