handle timezones

[mps9506]

new lubridate warning when no time zone is attached to the date column:

Error: Problem with `mutate()` input `temp`.
x 'origin' must be supplied
i Input `temp` is `purrr::map(...)`.
Run `rlang::last_error()` to see where the error occurred.
In addition: Warning message:
tz(): Don't know how to compute timezone for object of class numeric; returning "UTC". This warning will become an error in the next major version of lubridate. 

Example input data:

df <- structure(list(`End Date` = structure(c(13083, 13130, 13201, 
                                              13264, 13321, 13383, 13451, 13538, 13634, 13719, 13846, 13936, 
                                              14027, 14119, 14201, 14266, 14364, 14455, 14567, 14658, 14755, 
                                              14846, 14930, 15021, 15110, 15210, 15264, 15371, 15383, 15448, 
                                              15462, 15511, 15539, 15574, 15671, 15755, 15848, 15903, 16028, 
                                              16112, 16203, 16483, 16567, 16652, 16757, 16839, 16952, 17037, 
                                              17119, 17205, 17288, 17387, 17464, 17574, 17666, 17750, 17840
), class = "Date"), Value = c(5, 2420, 127, 370, 870, 28, 2400, 
                              2400, 520, 550, 2800, 2400, 46, 2400, 520, 2400, 2400, 580, 2400, 
                              2400, 6, 34, 2400, 330, 72, 6, 3, 24000, 4800, 110, 19, 2600, 
                              120, 310, 250, 2400, 2000, 190, 95, 4800, 4000, 2900, 74, 2, 
                              4800, 160, 220, 920, 120, 800, 360, 4800, 85, 2800, 84, 250, 
                              910)), row.names = c(NA, -57L), class = c("tbl_df", "tbl", "data.frame"
                              ))