Fat arrow hash syntax is better on some occasions

we may have a preference for using the new
hash syntax, and i use it on most occasions.
however, we must not have the build failing
for something that the language supports and
we don't prefer.

some good use cases for the fat arrow hash
just for enhanced readability because it
can represent a flow or connection are:

1. state machine transitions:

```transition :ready => :published```
reads better than
```transition ready: :published```

2. specifying joins in arel:

```joins(:document => :document_sources)```
reads better than
```joins(document: document_sources)```

also, i personally don't prefer seeing
both hash syntaxes used on the same line,
which this test forces me to write:

```joins(document_sources: :document)
     .where({'documents.id' => document.id})```
This gem was just for the test we removed
Merge pull request #1321 from alphagov/fat-arrow-hash-syntax-is-needed-at-times

Fat arrow hash syntax is better on some occasions