Corrected typo in examples for index_by

[mtkerbeR]

Furthermore, on the pkgdown page this example is not working: https://tsibble.tidyverts.org/reference/index-by.html#examples

Can reproduce this error message locally if library lubridate is not loaded

tourism %>% index_by(Year = ~ financial_year(.)) %>% summarise(Total = sum(Trips))

> Error: Problem with mutate() input Year.

> ✖ could not find function "financial_year"

> ℹ Input Year is f(Quarter).

[earowang]

Thanks.