Fix wrong link.

Author: recherst

README.md

@@ -86,7 +86,7 @@
 82. [Longest Palindrome](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/409.Longest%20Palindrome.playground/Contents.swift)
 83. [Fizz Buzz](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/409.Fizz%20Buzz.playground/Contents.swift)
 84. [Third Maximum Number](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/414.Third%20Maximum%20Number.playground/Contents.swift)
-85. [Add String](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/415.Add%20String.playground/Contents.swift)
+85. [Add Strings](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/415.Add%20Strings.playground/Contents.swift)
 
 #### Medium