Little change for backwards-compatibility

For Julia v 0.3.3, I tested "can__62.mtx" (symmetric sparse matrix) and "plsk1919.mtx" (Hermitian sparse matrix) and got error like:

` `Symmetric{T}` has no method matching Symmetric{T}(::SparseMatrixCSC{Bool,Int64}`

Then I tried to read them on Julia v 0.4.0, both matrices work fine here.  Thus I made this little change for compatibility.