doc: fix spelling of G Suite

'G Suite' seems to be the preferred spelling according to
https://gsuite.google.com/

Change-Id: Ica60938cf942594157bba84ef205e1cdcb8c1b08
Reviewed-on: https://go-review.googlesource.com/120132Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

doc/contribute.html

@@ -92,10 +92,10 @@ account to use.
 </p>
 
 <p>
-Google accounts can either be Gmail e-mail accounts, G-Suite organization accounts, or
+Google accounts can either be Gmail e-mail accounts, G Suite organization accounts, or
 accounts associated with an external e-mail address.
 For instance, if you need to use
-an existing corporate e-mail that is not managed through G-Suite, you can create
+an existing corporate e-mail that is not managed through G Suite, you can create
 an account associated
 <a href="https://accounts.google.com/SignUpWithoutGmail">with your existing
 e-mail address</a>.