[Fontinst] erratum in oms.etx

[Giuseppe Toscano]

Where it  reads

\setslot{wreathproduct}
    \comment{The Wreath product symbol `$\wp$'.}
\endsetslot

should be

\setslot{wreathproduct}
    \comment{The Wreath product symbol `$\wr$'.}
\endsetslot