docs(tutorial/index): fix spelling error for word 'standalone'

PR (#15187)

Author: pharkare

docs/content/tutorial/index.ngdoc

@@ -304,7 +304,7 @@ In that case, you can delete the `node_modules/` directory and run `npm install`
 <br />
 **Protractor dependencies**
 
-Under the hood, Protractor uses the [Selenium Stadalone Server][selenium], which in turn requires 
+Under the hood, Protractor uses the [Selenium Standalone Server][selenium], which in turn requires 
 the [Java Development Kit (JDK)][jdk] to be installed on your local machine. Check this by running 
 `java -version` from the command line.