message: Bump nlohmann json to 3.1.2
diff: @@ -8,11 +8,11 @@ readonly name="NLohmannJson"
  readonly ownership="JSON For Modern C++ Upstream <robot@adios2>"
  readonly subtree="thirdparty/NLohmannJson/json"
  readonly repo="https://github.com/nlohmann/json.git"
  -readonly tag="v2.1.1"
  +readonly tag="v3.1.2"
  readonly shortlog="true"
  readonly paths="
  LICENSE.MIT
  -src/json.hpp
  +single_include/nlohmann/json.hpp
  "
  extract_source () {
  