src: fix typo in probe description

This fixes a typo in a probe description added in
dc1996d.

PR-URL: nodejs/node#15397
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

src/v8ustack.d

@@ -522,7 +522,7 @@ dtrace:helper:ustack:
 		NO_SHARED_FUNCTION_NAME_SENTINEL;
 }
 
-dtracr:helper:ustack:
+dtrace:helper:ustack:
 /!this->done && this->hassharedname/
 {
 	LOAD_STRFIELDS(this->funcrawnamestr, this->funcnamelen,