Fix compilation error in createRandomMatrixOfRank()

test/main.h

diff --git a/test/main.h b/test/main.h
index 1574d53..aa6c4a3 100644
--- a/test/main.h
+++ b/test/main.h
@@ -230,7 +230,7 @@
 void createRandomMatrixOfRank(int desired_rank, int rows, int cols, Eigen::MatrixBase<Derived>& m)
 {
   typedef Derived MatrixType;
-  typedef MatrixType::Scalar Scalar;
+  typedef typename ei_traits<MatrixType>::Scalar Scalar;
   typedef Matrix<Scalar, MatrixType::ColsAtCompileTime, 1> VectorType;
 
   MatrixType a = MatrixType::Random(rows,rows);