Add previous versions back into package

Following the advice of @glennpj, added the old versions back into the
packages.

I can install the current packages and the previous packages.

var/spack/repos/builtin/packages/r-jsonlite/package.py

@@ -42,6 +42,7 @@ class RJsonlite(Package):
     list_url = "https://cran.r-project.org/src/contrib/Archive/jsonlite"
 
     version('1.0', 'c8524e086de22ab39b8ac8000220cc87')
+    version('0.9.21', '4fc382747f88a79ff0718a0d06bed45d')
 
     extends('R')