Update README.md

Author: gustavo-grieco

program-analysis/echidna/advanced/README.md

@@ -8,5 +8,5 @@
 - [How to test bytecode-only contracts](./testing-bytecode.md): How to fuzz a contract without bytecode or to perform differential fuzzing between Solidity and Vyper
 - [How to use hevm cheats to test permit](./hevm-cheats-to-test-permit.md): How to test code that depends on ecrecover signatures using hevm cheat codes
 - [How to seed Echidna with unit tests](./end-to-end-testing.md): How to use existing unit tests to seed Echidna
-- [how to fuzz contracts with external libraries](./working-with-libraries.md): How to fuzz a contract that has external libraries
+- [How to fuzz contracts with external libraries](./working-with-libraries.md): How to fuzz a contract that has external libraries
 - [Understanding and using `multi-abi`](./using-multi-abi.md): What is `multi-abi` testing, and how can it be used