Fix username in the github link

Author: ziishaned

Diff for: README.md

@@ -74,7 +74,7 @@ But knowing the stuff will help you become better! :muscle:*
 
 ### RegExp
 - [RegexHQ](https://github.com/regexhq)
-- [Learn regex the easy way](https://github.com/zeeshanu/learn-regex)
+- [Learn regex the easy way](https://github.com/ziishaned/learn-regex)
 
 ### Security
 - :book: [Security Programming](https://www.dwheeler.com/secure-programs/)