Fixed deprecated call

sensiolbas cookbook)
[2013-05-20T16:04:22+00:00] WARN: Setting attributes without specifying a
precedence is deprecated and will be removed in Chef 11.0. To set attributes
at normal precedence, change code like:
`node["key"] = "value"` # Not this to:
`node.set["key"] = "value"` # This

Called from:
 /var/chef/cache/cookbooks/wal_e/recipes/default.rb:17:in `from_file'