Fix syntax error

Apparently, the previous code is not valid.

[Thu, 30 Jan 2014 13:25:37 +0100] FATAL: SyntaxError: compile error
/var/chef/cache/cookbooks/swift/recipes/proxy.rb:117: syntax error, unexpected tSTRING_BEG, expecting '}'
...bled" => node.roles.include? "ceilometer-swift-proxy-middlew...
                              ^
/var/chef/cache/cookbooks/swift/recipes/proxy.rb:117: syntax error, unexpected '}', expecting $end