Fix encoding of string on Ruby 2.7

Author: jhawthorn

ext/rapidjson/extconf.rb

@@ -14,6 +14,6 @@
 $LDFLAGS += " -fsanitize=address"
 end
 
-have_func("rb_interned_str", "ruby.h")
+have_func("rb_enc_interned_str", "ruby.h")
 
 create_makefile("rapidjson/rapidjson")

ext/rapidjson/parser.hh

@@ -63,10 +63,10 @@ struct RubyObjectHandler : public BaseReaderHandler<UTF8<>, RubyObjectHandler> {
     }
 
     bool Key(const char* str, SizeType length, bool copy) {
-#ifdef HAVE_RB_INTERNED_STR
+#ifdef HAVE_RB_ENC_INTERNED_STR
         VALUE val = rb_enc_interned_str(str, length, rb_utf8_encoding());
 #else
-        VALUE val = rb_str_new(str, length);
+        VALUE val = rb_enc_str_new(str, length, rb_utf8_encoding());
 #endif
         return PutKey(val);
     }