very temporary fix of user agent problems in #22

[balthasars]

temporary fix of #22. I am equally confused as the other users with regard to how to successfully set the environmental variable EDGARWEBR_USER_AGENT — for some reason I was unsuccessful with both usethis::edit_r_environ() and Sys.setenv(). I'm sure there is a better solution, but this makes it easier to get the package running again.