Precision issue in JsonFloat serialization

Created by: pgn69

Serializing certain float numbers the result contains unexpected decimals.

Test case:

  StaticJsonBuffer<128> jsonBuffer;
  JsonObject& jsonObject = jsonBuffer.createObject();
  
  float x = 999.9;
  jsonObject["x"] = x;

  jsonObject.printTo(Serial);
  Serial.println();

The output is:

{"x":999.900024}

• Target platform: Bluno Nano SKU:DFR0296, based on Atmega328
• Compiler version: 4.9.2