Fix MUSIC_DIRECTORY_SERVE_PATH example value in configuration.rst

Status Job ID Name Coverage
  Lint
passed #4127
black

00:00:38

passed #4128
flake8

00:00:30

 
  Test
passed #4129
docker
test_api

00:03:16

passed #4227
docker
test_front

00:02:19

failed #4130
docker
test_front

00:03:45

failed #4222
docker
test_front

00:05:04