[Rd] trivial typo in ?Matrix::sparse.model.matrix.Rd

[Ben Bolker]

   "form" -> "from". Diff against latest SVN:

Index: sparse.model.matrix.Rd
===================================================================
--- sparse.model.matrix.Rd    (revision 3336)
+++ sparse.model.matrix.Rd    (working copy)
@@ -4,7 +4,7 @@
  \alias{fac2sparse}
  \alias{fac2Sparse}
  \description{Construct a sparse model or \dQuote{design} matrix,
-  form a formula and data frame (\code{sparse.model.matrix}) or a single
+  from a formula and data frame (\code{sparse.model.matrix}) or a single
    factor (\code{fac2sparse}).

    The \code{fac2[Ss]parse()} functions are utilities, also used