improve isIPv4 perf

Author: Uzlopak

lib/internal/net.js

@@ -12,7 +12,7 @@ const errors = require('internal/errors');
 
 // IPv4 Segment
 const v4Seg = '(?:[0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])';
-const v4Str = `(${v4Seg}[.]){3}${v4Seg}`;
+const v4Str = `(?:${v4Seg}[.]){3}${v4Seg}`;
 const IPv4Reg = new RegExp(`^${v4Str}$`);
 
 // IPv6 Segment