Fixed example in addon.md. (#820)

PR-URL: nodejs/node-addon-api#820
Reviewed-By: Michael Dawson <[email protected]>
Reviewed-By: Gabriel Schulhof <[email protected]>

doc/addon.md

@@ -41,9 +41,9 @@ class ExampleAddon : public Napi::Addon<ExampleAddon> {
 
       // We can also attach plain objects to `exports`, and instance methods as
       // properties of those sub-objects.
-      InstanceValue("subObject", DefineProperties(Napi::Object::New(), {
-        InstanceMethod("decrement", &ExampleAddon::Decrement
-      })), napi_enumerable)
+      InstanceValue("subObject", DefineProperties(Napi::Object::New(env), {
+        InstanceMethod("decrement", &ExampleAddon::Decrement)
+      }), napi_enumerable)
     });
   }
  private:
@@ -80,7 +80,7 @@ The above code can be used from JavaScript as follows:
 const exampleAddon = require('bindings')('example_addon');
 console.log(exampleAddon.increment()); // prints 43
 console.log(exampleAddon.increment()); // prints 44
-consnole.log(exampleAddon.subObject.decrement()); // prints 43
+console.log(exampleAddon.subObject.decrement()); // prints 43
 ```
 
 When Node.js loads an instance of the add-on, a new instance of the class is