PlatformIO build_flags docs issue

main.cpp

#include <Arduino.h>

#include <ESP8266WiFi.h>  //https://github.com/esp8266/Arduino
#include <DNSServer.h>
#include <ESP8266mDNS.h>
#include <ESP8266WebServer.h>
#include <ArduinoOTA.h>

#define SSID "fancy-ssid"
#define PASS "pass"
//#define DEVICE_HOSTNAME "tracer-1"

void setup() {
  WiFi.begin(SSID,PASS);

  MDNS.begin(DEVICE_HOSTNAME);
  
  ArduinoOTA.setHostname(DEVICE_HOSTNAME);
  ArduinoOTA.begin();
}

void loop() {
  MDNS.update();
  ArduinoOTA.handle();
}

platformio.ini

[env:tracer]
platform = espressif8266
board = nodemcuv2
framework = arduino
build_flags = -DDEVICE_HOSTNAME="tracer"

[env:tracer-1]
platform = espressif8266
board = nodemcuv2
framework = arduino
build_flags = -DDEVICE_HOSTNAME="tracer-1"

[env:tracer-2]
platform = espressif8266
board = nodemcuv2
framework = arduino
build_flags = '-DDEVICE_HOSTNAME="tracer-2"'