Add a todo about missing version in rollbacks

spec/offchain.tex

@@ -298,7 +298,7 @@ \subsection{Rollbacks and protocol changes}\label{sec:rollbacks}
 wrapped in a rollforward event $(\mathtt{rollback},p)$ with point $p$, protocol
 participants store their head state indexed by this point in a history
 $\Omega$ of states
-$\Delta \gets (\hats, \bar{\mc S}.s, \bar{\mc S}.sigma, \hatmU, \barmU, \hatSigma, \hatmL, \hatmT)$ and $\Omega' = (p, \Delta) \cup \Omega$. \\
+\todo{add version here also}$\Delta \gets (\hats, \bar{\mc S}.s, \bar{\mc S}.sigma, \hatmU, \barmU, \hatSigma, \hatmL, \hatmT)$ and $\Omega' = (p, \Delta) \cup \Omega$. \\
 
 \dparagraph{$\mathtt{rollback}$.}\quad On a rollback
 $(\mathtt{rollback},p_{rb})$ to point $p_{rb}$, the corresponding head state