Merge pull request #575 from brookslogan/make_covidcast_endpoint_default_format_arg_work_in_R_client

Use `match.arg` on covidcast endpoint `format` argument in R client

Author: krivard

src/client/delphi_epidata.R

@@ -521,6 +521,7 @@ Epidata <- (function() {
     if(!missing(issues) && !missing(lag)) {
       stop('`issues` and `lag` are mutually exclusive')
     }
+    format <- match.arg(format)
     # Set up request
     params <- list(
       endpoint = 'covidcast',