Fix typo for new RequireNullCoalesceEqualOperator flag

Author: jnoordsij

doc/control-structures.md

@@ -194,7 +194,7 @@ Requires use of null coalesce equal operator when possible.
 This sniff provides the following setting:
 
 * `enable`: either to enable or not this sniff. By default, it is enabled for PHP versions 7.4 or higher.
-* `checkIfCondition` (default: `false`): will check `if` conditions too.
+* `checkIfConditions` (default: `false`): will check `if` conditions too.
 
 #### SlevomatCodingStandard.ControlStructures.RequireNullCoalesceOperator 🔧