fix: typo in implementation details (#24)

Author: bitttttten

exercises/01.principles/02.solution.implementation-details/README.mdx

@@ -33,7 +33,7 @@ To that, I want to share a quote with you:
 
 <callout-info class="important">The implementation may change but the intention stays the same.</callout-info>
 
-You write tests to cement the intentions you have. Deciphering those intentions from ther source code alone can proof challenging and, at times, dangerous. Remember that the code you are working with _may not have been written by you_. It could've been a colleague who's now on vacation, or have left the company long before you joined. But you have to debug and fix the code right now. For that, you have to know what was the intention behind that code.
+You write tests to cement the intentions you have. Deciphering those intentions from the source code alone can prove challenging and, at times, dangerous. Remember that the code you are working with _may not have been written by you_. It could've been a colleague who's now on vacation, or have left the company long before you joined. But you have to debug and fix the code right now. For that, you have to know what was the intention behind that code.
 
 This is where automated tests can be a life-changing factor. They act as a partial documentation for the code, and make things like code refactoring (i.e. changing the implementation) _much_ easier.