Issue title: Sequential type annotations should have blank space between them.
 Issue body: 
```elm
encode : Stats -> Json.Encode.Value
decoder : Json.Decode.Decoder Stats
```
should format with two blank lines in between.
 Comments: 
 Comment 0: Might have been fixed by d63a2f728c89ee0e6d7fed2b9ead4afb47248793.
 Comment 1: Backfilled tests in c1fead4.
{'source': 'GithubIssues', 'repo_name_with_owner': 'avh4/elm-format', 'issue_id': 127071806, 'repo_stars': 1424.0}