Revert switch to jsonlite

This reverts commits deffc90, ab4dc64, and 0755579, returning to RJSONIO.
The purpose of this is to prepare for a maintenance release for 0.11
without the switch to jsonlite, to reduce the risk of new bugs.

NAMESPACE

@@ -196,3 +196,4 @@ import(htmltools)
 import(httpuv)
 import(mime)
 import(xtable)
+importFrom(RJSONIO,fromJSON)