fix minor typo in coding guidelines

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@42684 65c4cc65-6c06-0410-ace0-fbb531ad65f3

doc/CODING-GUIDELINES

@@ -170,7 +170,7 @@ Instead, try to minimize the number of lines of code that need to be
 indented, by only indenting the shortest case of the 'if'
 statement, like so:
 
-if !(foo) {
+if (!foo) {
 	result = 0;
 	return;
 }