config/advice.txt: fix description list separator

The whole submoduleAlternateErrorStrategyDie item is interpreted as
being part of the supporting content of the preceding item. This is
because we don't give a double-colon "::" for the separator, but just a
single colon, ":". Let's fix that.

There are a few other matches for [^:]:\s*$ in Documentation/config, but
I didn't spot any similar bugs among them.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/advice.txt

@@ -107,7 +107,7 @@ advice.*::
 		editor input from the user.
 	nestedTag::
 		Advice shown if a user attempts to recursively tag a tag object.
-	submoduleAlternateErrorStrategyDie:
+	submoduleAlternateErrorStrategyDie::
 		Advice shown when a submodule.alternateErrorStrategy option
 		configured to "die" causes a fatal error.
 --