Include <string_view> in "nlohmann/json.hpp" when C++17 is used

include/nlohmann/json.hpp

@@ -73,6 +73,10 @@ SOFTWARE.
 #include <nlohmann/json_fwd.hpp>
 #include <nlohmann/ordered_map.hpp>
 
+#if defined(JSON_HAS_CPP_17)
+    #include <string_view>
+#endif
+
 /*!
 @brief namespace for Niels Lohmann
 @see https://github.com/nlohmann

single_include/nlohmann/json.hpp

@@ -16663,6 +16663,10 @@ template <class Key, class T, class IgnoredLess = std::less<Key>,
 }  // namespace nlohmann
 
 
+#if defined(JSON_HAS_CPP_17)
+    #include <string_view>
+#endif
+
 /*!
 @brief namespace for Niels Lohmann
 @see https://github.com/nlohmann

test/src/unit-conversions.cpp

@@ -48,10 +48,6 @@ using nlohmann::json;
     #define JSON_HAS_CPP_14
 #endif
 
-#if defined(JSON_HAS_CPP_17)
-    #include <string_view>
-#endif
-
 TEST_CASE("value conversion")
 {
     SECTION("get an object (explicit)")