Fix stub deprecation warning

Deprecation Warnings:

Using `stub` from rspec-mocks' old `:should` syntax without explicitly enabling the syntax is deprecated. Use the new `:expect` syntax or explicitly enable `:should` instead. Called from /workspace/spec/classes/storm/namespace.xml.erb_spec.rb:69:in `block (2 levels) in <top (required)>'.

spec/classes/storm/namespace.xml.erb_spec.rb

@@ -65,14 +65,14 @@
   end
 
   before(:each) do
-    scope.stub(:lookupvar).with('storm::backend::storage_areas').and_return(storage_areas)
-    scope.stub(:lookupvar).with('storm::backend::gsiftp_pool_members').and_return(gsiftp_pool_members)
-    scope.stub(:lookupvar).with('storm::backend::webdav_pool_members').and_return(webdav_pool_members)
-    scope.stub(:lookupvar).with('storm::backend::fs_type').and_return(nil)
-    scope.stub(:lookupvar).with('storm::backend::xroot_hostname').and_return('storm.example.org')
-    scope.stub(:lookupvar).with('storm::backend::xroot_port').and_return(1094)
-    scope.stub(:lookupvar).with('storm::backend::gsiftp_pool_balance_strategy').and_return('round-robin')
-    scope.stub(:lookupvar).with('storm::backend::webdav_pool_balance_strategy').and_return('round-robin')
+    allow(scope).to receive(:lookupvar).with('storm::backend::storage_areas').and_return(storage_areas)
+    allow(scope).to receive(:lookupvar).with('storm::backend::gsiftp_pool_members').and_return(gsiftp_pool_members)
+    allow(scope).to receive(:lookupvar).with('storm::backend::webdav_pool_members').and_return(webdav_pool_members)
+    allow(scope).to receive(:lookupvar).with('storm::backend::fs_type').and_return(nil)
+    allow(scope).to receive(:lookupvar).with('storm::backend::xroot_hostname').and_return('storm.example.org')
+    allow(scope).to receive(:lookupvar).with('storm::backend::xroot_port').and_return(1094)
+    allow(scope).to receive(:lookupvar).with('storm::backend::gsiftp_pool_balance_strategy').and_return('round-robin')
+    allow(scope).to receive(:lookupvar).with('storm::backend::webdav_pool_balance_strategy').and_return('round-robin')
   end
 
   it 'render the same file each time' do