Update Input_Validation_Cheat_Sheet.md missing capitalisation. (#1604)

Correcting missing capitalisation.

cheatsheets/Input_Validation_Cheat_Sheet.md

@@ -41,7 +41,7 @@ Plus, such filters frequently prevent authorized input, like `O'Brian`, where th
 
 While denylisting can be useful as an additional layer of defense to catch some common malicious patterns, it should not be relied upon as the primary method. Allowlisting remains the more robust and secure approach for preventing potentially harmful input.
 
-Allowlist validation is appropriate for all input fields provided by the user. allowlist validation involves defining exactly what IS authorized, and by definition, everything else is not authorized.
+Allowlist validation is appropriate for all input fields provided by the user. Allowlist validation involves defining exactly what IS authorized, and by definition, everything else is not authorized.
 
 If it's well structured data, like dates, social security numbers, zip codes, email addresses, etc. then the developer should be able to define a very strong validation pattern, usually based on regular expressions, for validating such input.