When did you installed this library? The Json library was renamed to ArduinoJson. Please uninstall current libraries and try again. See my log
pio lib -g install Homie
Library Storage: /Users/ikravets/.platformio/lib
Looking for Homie library in registry
Found: http://platformio.org/lib/show/555/Homie
LibraryManager: Installing id=555
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Homie @ 1.5.0 has been successfully installed!
Installing dependencies
Looking for ArduinoJson library in registry
Found: http://platformio.org/lib/show/64/ArduinoJson
LibraryManager: Installing id=64
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ArduinoJson @ 5.6.6 has been successfully installed!
Looking for PubSubClient library in registry
Found: http://platformio.org/lib/show/89/PubSubClient
LibraryManager: Installing id=89
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PubSubClient @ 2.6 has been successfully installed!
Looking for Bounce2 library in registry
Found: http://platformio.org/lib/show/1106/Bounce2
LibraryManager: Installing id=1106
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Bounce2 @ 2.1 has been successfully installed!