Missing description of the last_update field

[tinatownes]

Problem: Notice it's missing a description of the last_update field. Also last_update # is in the wrong format. It should be a date, but it's numeric. Need to file an issue # either in epidatr or in delphi-epidata, plus update the documentation page.

Fix: meta$last_update <- as.POSIXct(meta$last_update, origin = "1970-01-01")

[nmdefries]

Which endpoint or function is this referring to? Are we missing documentation of the function argument or of a column in the returned data frame?

[nmdefries]

Problem with how covidcast metadata last_update field is formatted. Supposed to be a date, but is returned as an int (seconds or minutes since epoch).

Also missing from documentation website -- split out into separate issue in delphi-epidata and tag Tina.