Update stdlib dependency to 4.x

puppetlabs/stdlib 4.x is backwards compatible with 3.x and still tested
on Puppet 2.7. Updating stdlib to 4.x allows modules to use newer
functions without breaking older functionality.

Change-Id: Ia100f0bde5a27fb4a28d3918742460163305dd8c

Modulefile

@@ -10,7 +10,7 @@ source       'https://github.com/stackforge/puppet-neutron'
 dependency 'puppetlabs/inifile', '>=1.0.0 <2.0.0'
 dependency 'puppetlabs/keystone', '>=4.0.0 <5.0.0'
 dependency 'puppetlabs/nova', '>=4.0.0 <5.0.0'
-dependency 'puppetlabs/stdlib', '>=3.2.0'
+dependency 'puppetlabs/stdlib', '>=4.0.0 <5.0.0'
 dependency 'puppetlabs/vswitch', '>=0.2.0 <1.0.0'
 dependency 'duritong/sysctl', '>=0.0.1 <1.0.0'
 dependency 'stackforge/openstacklib', '>=5.0.0'