fix capabilities

[saschalippert]

capabilities need to be returned as array, else it is interpreted as ["b","o","d","y"]

further i recommend to return even more capabilities, else some programs like eg brave will refuse to use your notification service

example which works for me and brave:

return (["actions", "body", "body-hyperlinks", "body-markup", "icon-static", "x-canonical-private-icon-only"])