Doc: fix formatting of a gui item by adding curly braces

Change-Id: I78a8bd6aecd853e5436b259705044747c8cd8c9b
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@nokia.com>

doc/src/projects/creator-projects-settings-code-style.qdoc

@@ -54,7 +54,7 @@
 
         \o  Select \gui {Projects > Code Style Settings}.
 
-        \o  In the \gui Language field, select \gui C++ or \gui Qt Quick.
+        \o  In the \gui Language field, select \gui C++ or \gui {Qt Quick}.
 
         \o  In the \gui {Current settings} field, select the settings to modify
             and click \gui Copy.