commands/plugin: old state files default to 0 for vagrant version

plugins/commands/plugin/state_file.rb

@@ -64,7 +64,9 @@ module VagrantPlugins
 
         new_installed = {}
         (@data["installed"] || []).each do |plugin|
-          new_installed[plugin] = {}
+          new_installed[plugin] = {
+            "vagrant_version" => "0",
+          }
         end
 
         @data["installed"] = new_installed

test/unit/plugins/commands/plugin/state_file_test.rb

@@ -61,7 +61,9 @@ describe VagrantPlugins::CommandPlugin::StateFile do
     end
 
     it "should have the right installed plugins" do
-      subject.installed_plugins.keys.should eql(["foo"])
+      plugins = subject.installed_plugins
+      expect(plugins.keys).to eql(["foo"])
+      expect(plugins["foo"]["vagrant_version"]).to eql("0")
     end
   end
 end