Fix #6269 - Hashes only work with two levels of access

The following manifest was failing:

$hash = { 'a' => { 'b' => { 'c' => 'it works' } } }
$out = $hash['a']['b']['c']

because of a typo in the grammar.

Signed-off-by: Brice Figureau <brice-puppet@daysofwonder.com>