Update dead cognitive-complexity link (#569)

Author: jmckenzieark

RULES_DESCRIPTIONS.md

@@ -136,7 +136,7 @@ _Configuration_: N/A
 
 ## cognitive-complexity
 
-_Description_: [Cognitive complexity](https://www.sonarsource.com/resources/white-papers/cognitive-complexity.html) is a measure of how hard code is to understand. 
+_Description_: [Cognitive complexity](https://www.sonarsource.com/docs/CognitiveComplexity.pdf) is a measure of how hard code is to understand.
 While cyclomatic complexity is good to measure "testability" of the code, cognitive complexity aims to provide a more precise measure of the difficulty of understanding the code.
 Enforcing a maximum complexity per function helps to keep code readable and maintainable.