message: Fix stale links to cppreference.com concepts.
diff: @@ -39,7 +39,7 @@ class WeightedQuantilesSummary {
  // Explicitly initialize all of memory (including padding from memory
  // alignment) to allow the struct to be msan-resistant "plain old data".
  //
  - // POD = http://en.cppreference.com/w/cpp/concept/PODType
  + // POD = https://en.cppreference.com/w/cpp/named_req/PODType
  memset(this, 0, sizeof(*this));
  value = v;
  