Make python examples PEP8 compliant.

These are my proposed fixes for rethinkdb/rethinkdb#2534.
The old example above is a `SyntaxError` with the `.` at the end of the line or after the newline. Inside parenthesis as @AtnNn likes does fix the `SyntaxError`.

I dislike the syntax presented for two reasons.

  - It adds Python control symbols to all ReQL statements.
  - It promotes indentation that is not a multiple of 4 spaces.

The 4 spaces is a more personal nit pick, so if consensus is against me then I will drop it.
Adding parenthesis means that the statement is dependent on its context. If I write a subquery in `branch` expression, then I cannot move that subquery out of the containing query without remembering that the subquery must now have parenthesis added.