C++: Fix QLDoc comment

Author: jketema

cpp/ql/lib/semmle/code/cpp/regex/RegexTreeView.qll

@@ -1238,7 +1238,7 @@ private module Impl implements RegexTreeViewSig {
   }
 
   /**
-   * Holds if `root` has the `s` flag for multi-line matching.
+   * Holds if `root` has the `s` flag for dot-all matching.
    */
   predicate isDotAll(RegExpTerm root) {
     root.isRootTerm() and

cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll

@@ -14,7 +14,7 @@ private import semmle.code.cpp.exprs.Literal
  */
 abstract class RegExp extends StringLiteral {
   /**
-   * Holds if this `RegExp` has the `s` flag for multi-line matching.
+   * Holds if this `RegExp` has the `s` flag for dot-all matching.
    */
   predicate isDotAll() { none() }