Fix service double stubbing

MSP-13484

spec/lib/msf/core/exploit/http/server_spec.rb

@@ -16,11 +16,9 @@ RSpec.describe Msf::Exploit::Remote::HttpServer do
   end
 
   let(:mock_service) do
-    mock_service = double 'service',
+    double 'service',
            add_resource: nil,
-                          :'server_name' => nil
-
-    mock_service
+           :'server_name=' => nil
   end
 
   before do