message: use b_string instead of b_utf8
diff: @@ -22,7 +22,7 @@ namespace {
  using namespace bsoncxx;
  using bsoncxx::types::b_int32;
  -using bsoncxx::types::b_utf8;
  +using bsoncxx::types::b_string;
  using types::bson_value::make_value;
  TEST_CASE("array element lookup with std::find", "[bsoncxx::array::view]") {
  @@ -42,14 +42,14 @@ TEST_CASE("array element lookup with std::find", "[bsoncxx::array::view]") {
  SECTION("non-matching utf8 elements") {
  builder::basic::array a_builder;
  - a_builder.append(b_utf8{"yes"}, b_utf8{"no"});
  + a_builder.append(b_string{"yes"}, b_string{"no"});
  auto a = a_builder.view();
  REQUIRE(std::find(a.cbegin(), a.cend(), val) == a.cend());
  }
  SECTION("array with one matching element") {
  builder::basic::array a_builder;
  - a_builder.append(b_utf8{"yes"}, b_utf8{"no"}, b_utf8{"hello"});
  + a_builder.append(b_string{"yes"}, b_string{"no"}, b_string{"hello"});
  auto a = a_builder.view();
  auto it = std::find(a.cbegin(), a.cend(), val);
  REQUIRE(it != a.cend());
  @@ -58,7 +58,7 @@ TEST_CASE("array element lookup with std::find", "[bsoncxx::array::view]") {
  SECTION("array with multiple matching elements") {
  builder::basic::array a_builder;
  - a_builder.append(b_utf8{"yes"}, b_utf8{"hello"}, b_utf8{"hello"});
  + a_builder.append(b_string{"yes"}, b_string{"hello"}, b_string{"hello"});
  auto a = a_builder.view();
  auto it = std::find(a.cbegin(), a.cend(), val);
  REQUIRE(it != a.cend());
  