Fix find-doc-nits: { is significant in regexps

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3019)

util/find-doc-nits

@@ -96,7 +96,7 @@ sub name_synopsis()
         } elsif ( $line =~ /typedef.* (\S+);/ ) {
             # a simple typedef: typedef ... NAME;
             $sym = $1;
-        } elsif ( $line =~ /enum (\S*) {/ ) {
+        } elsif ( $line =~ /enum (\S*) \{/ ) {
             # an enumeration: enum ... {
             $sym = $1;
         } elsif ( $line =~ /#define ([A-Za-z0-9_]+)/ ) {