Dubbo

Minor changes

• The internal stations_site_list now is checked against GADM
  (Global Administrative Areas), http://www.gadm.org/ to ensure state listed is
  correct. This is in response to an error where Alice Springs Airport was
  reported in South Australia in the March 2018 update from BOM. There may be
  others. The original BOM values for state are in an org_state column.
  However, bomrang will use the corrected state column values.

• Update code to be compliant with current and future versions of janitor

Bug fixes

• Correct issue with converting the timzeone in ag bulletin to character where
  the conversion resulted in a vector of numerals, not the expected string of
  characters, e.g. "EST"

• Remove redundant functionality in update_station_locations() where data were
  fetched using tryCatch() and then again without