Fix formatting of example blocks

With the new stylesheet example blocks (delimited with ====) are
rendered as rather intrusive boxes with large padding in yellow
and grey.

This patch replaces the example blocks with simple code blocks
(delimited with ----) that better match the overall style of the
documentation.

Change-Id: Id95387cdb153332c2066e2d5e378697647dbca52
Signed-off-by: Michael Ochmann <michael.ochmann@sap.com>

Documentation/cmd-ls-groups.txt

@@ -87,55 +87,55 @@ nonexistent group, the owner group name field will read `n/a`.
 == EXAMPLES
 
 List visible groups:
-=====
+----
 	$ ssh -p 29418 review.example.com gerrit ls-groups
 	Administrators
 	Anonymous Users
 	MyProject_Committers
 	Project Owners
 	Registered Users
-=====
+----
 
 List all groups for which any permission is set for the project
 "MyProject":
-=====
+----
 	$ ssh -p 29418 review.example.com gerrit ls-groups --project MyProject
 	MyProject_Committers
 	Project Owners
 	Registered Users
-=====
+----
 
 List all groups which are owned by the calling user:
-=====
+----
 	$ ssh -p 29418 review.example.com gerrit ls-groups --owned
 	MyProject_Committers
 	MyProject_Verifiers
-=====
+----
 
 Check if the calling user owns the group `MyProject_Committers`. If
 `MyProject_Committers` is returned the calling user owns this group.
 If the result is empty, the calling user doesn't own the group.
-=====
+----
 	$ ssh -p 29418 review.example.com gerrit ls-groups --owned -q MyProject_Committers
 	MyProject_Committers
-=====
+----
 
 Extract the UUID of the 'Administrators' group:
 
-=====
+----
 	$ ssh -p 29418 review.example.com gerrit ls-groups -v | awk '-F\t' '$1 == "Administrators" {print $2}'
 	ad463411db3eec4e1efb0d73f55183c1db2fd82a
-=====
+----
 
 Extract and expand the multi-line description of the 'Administrators'
 group:
 
-=====
+----
 	$ printf "$(ssh -p 29418 review.example.com gerrit ls-groups -v | awk '-F\t' '$1 == "Administrators" {print $3}')\n"
 	This is a
 	multi-line
 	description.
-=====
+----
 
 GERRIT
 ------