AK: Use new format functions.

Author: https://github.com/asynts
Commit: 1d96d5eea4
Pull-request: https://github.com/SerenityOS/serenity/pull/3705
Reviewed-by: https://github.com/awesomekling

AK/JsonObject.h

@@ -182,7 +182,7 @@ inline void JsonValue::serialize(Builder& builder) const
                 builder.append("\\\\");
                 break;
             default:
-                builder.appendf("%c", ch);
+                builder.append(ch);
             }
         }
         builder.append("\"");
@@ -202,16 +202,16 @@ inline void JsonValue::serialize(Builder& builder) const
         break;
 #endif
     case Type::Int32:
-        builder.appendf("%d", as_i32());
+        builder.appendff("{}", as_i32());
         break;
     case Type::Int64:
-        builder.appendf("%lld", as_i64());
+        builder.appendff("{}", as_i64());
         break;
     case Type::UnsignedInt32:
-        builder.appendf("%u", as_u32());
+        builder.appendff("{}", as_u32());
         break;
     case Type::UnsignedInt64:
-        builder.appendf("%llu", as_u64());
+        builder.appendff("{}", as_u64());
         break;
     case Type::Null:
         builder.append("null");