Fix definition of parallels? (#174)

Parallels Desktop appears as node['virtualization']['systems'] == 'parallels' not 'Parallels'

lib/chef/sugar/virtualization.rb

@@ -55,7 +55,7 @@ class Chef
       #   otherwise
       #
       def parallels?(node)
-        node.key?('virtualization') && node['virtualization']['system'] == 'Parallels'
+        node.key?('virtualization') && node['virtualization']['system'] == 'parallels'
       end
 
       #

spec/unit/chef/sugar/virtualization_spec.rb

@@ -39,7 +39,7 @@ describe Chef::Sugar::Virtualization do
 
   describe '#parallels?' do
     it 'returns true when the machine is under parallels' do
-      node = { 'virtualization' => { 'system' => 'Parallels' } }
+      node = { 'virtualization' => { 'system' => 'parallels' } }
       expect(described_class.parallels?(node)).to be true
     end