Update downloadingAndInstalling.adoc

Trivial update. 

Capitalization was incorrect in expected output.

The CLI does not support -version, but does support --version.

src/en/guide/gettingStarted/downloadingAndInstalling.adoc

@@ -49,9 +49,9 @@ Start + R
 ** Edit the Path variable on User Variables / System Variables depending on your choice.
 ** Paste the copied path in the Path Variable.
 
-If Grails is working correctly you should now be able to type `grails -version` in the terminal window and see output similar to this:
+If Grails is working correctly you should now be able to type `grails --version` in the terminal window and see output similar to this:
 
 [source,groovy,subs="attributes+"]
 ----
-Grails version: {version}
+Grails Version: {version}
 ----