(GH-646) Use Package[sensu], not Package[Sensu] on Windows

Partially resolves #646

Still running into this error:

    Error: Parameter ensure failed on Package[sensu]: Provider windows
    must have features 'upgradeable' to set 'ensure' to 'latest' at
    sensu/manifests/package.pp:64

manifests/package.pp

@@ -45,8 +45,8 @@
       $repo_require = undef
 
       $pkg_version = inline_template("<%= scope.lookupvar('sensu::version').sub(/(.*)\\-/, '\\1.') %>")
-      $pkg_title = 'Sensu'
-      $pkg_name = 'Sensu'
+      $pkg_title = 'sensu'
+      $pkg_name = 'sensu'
       $pkg_source = "C:\\Windows\\Temp\\sensu-${sensu::version}.msi"
       $pkg_require = "Remote_file[${pkg_source}]"