Update README.md

Author: crynobone

README.md

@@ -65,7 +65,7 @@ To reverse the above action, you need to run the following command:
 php vendor/bin/testbench nova:devtool disable-vue-devtool
 ```
 
-## Ugrading from Nova 4
+## Upgrading from Nova 4
 
 Nova Devtool ships with a generic `nova.mix.js` instead of publishing the file on each 3rd-party components. For external 3rd-party component you just need to include change the following code in `webpack.mix.js`: