Fix 'wide' environment

For me, the current version of the wide environment results in an error about "missing number, treated as zero" and "Illegal unit of measurement", so it does not compile if I use the \begin{wide}...\end{wide}. These changes made it work for me.

Assigning @mschmittner as he wrote the original code - was I doing something wrong / is there any reason not to do it in this new way? It is based on this tex.SE answer.