Switch stance on line-based coding style

This change will help to minimize the number of changes to adjacent
lines, which will allow for more productive use of tools like `git
blame`.

By preferring a trailing comma on the end of the last item in of an
Array or Hash literal, changes will be restricted to a single line
because each future line will be syntactically complete. To be better
explain, consider a Hash with 2 keys:

{
  foo: 'bar',
  baz: 'qux'
}

In order to add another key/value pair to this Hash, we would have to
change 2 lines:

{
  foo: 'bar',
  baz: 'qux',
  quux: 'corge'
}

Specifically, we must add a comma to the previous key/value pair and
then add the key/value pair--changes on two lines.

With this proposed change in place, the above Hash would instead be
declared like so:

{
  foo: 'bar',
  baz: 'qux',
}

Which would simplify the effort needed to incorporate another key/value
pair anywhere in the Hash. Now, to add the same key/value pair to the
Hash, we only need to modify one line:

{
  foo: 'bar',
  baz: 'quz',
  quux: 'corge',
}

Further reading:

- http://mislav.uniqpath.com/2014/02/hidden-documentation/
- https://gist.github.com/isaacs/357981#comment-397