Add JSON validation back in once jsonlite is updated

[jeremystan]

'jsonlite::validate' leaves global error data that is picked up later by 'jsonlite::fromJSON' for JSON 'false' values. See resolved issue for 'jsonlite' here: jeroen/jsonlite#49

Once that issue is released, need to update dependencies and add JSON validation back in, reversing this commit:

(ds)MBP0366:tidyjson jeremystanley$ git diff HEAD~1
diff --git a/R/tbl_json.r b/R/tbl_json.r
index 161dd15..c957234 100644
--- a/R/tbl_json.r
+++ b/R/tbl_json.r
@@ -50,12 +50,6 @@ as.tbl_json.tbl_json <- function(x, ...) x
 #' @export
 as.tbl_json.character <- function(x, ...) {

-  # Check for valid
-  is_valid <- vapply(x, validate, logical(1))
-
-  if (any(!is_valid))
-    stop(sprintf("%s records have invalid json data", sum(!is_valid)))
-
   # Parse the json
   json <- lapply(x, fromJSON, simplifyVector = FALSE)