Fix JSON example

This works again:

    Idris> :load examples/Json.idr
    *examples/Json> parse jsonValue "{\n  \"c"hallo\":42,\"nichts\":null}"
    Right (JsonObject (M 1
                         (Branch2 (Leaf "hallo" (JsonNumber 42.0))
                                  "hallo"
                                  (Leaf "nichts" JsonNull)))) : Either String
                                                                       JsonValue

I hope this solves https://github.com/ziman/lightyear/issues/10.