xorR is broken in chisel-tutorial

[adoerflinger]

I observed that the xorR operator is broken when used within this tutorial which I think is due to an old FIRRTL backend as described in:
chipsalliance/treadle#78

Now I tried to update the FIRRTL (and chisel version) in the build.sbt, however this results in several errors of the PeekPokeTester. Would it be possible to update this tutorial to use the current FIRRTL and chisel?

Regards
Alex