Increase the tolerance in sparse_cholesky_test

The current tolerance is too strict and causes failures on
Windows7 x64 with mingw64.

https://github.com/ceres-solver/ceres-solver/issues/315

Change-Id: Idf6f5e50ac61c36a35d7a576af6c88c6d1609869

internal/ceres/sparse_cholesky_test.cc

diff --git a/internal/ceres/sparse_cholesky_test.cc b/internal/ceres/sparse_cholesky_test.cc
index 60dae64..4c1f6d8 100644
--- a/internal/ceres/sparse_cholesky_test.cc
+++ b/internal/ceres/sparse_cholesky_test.cc
@@ -143,7 +143,7 @@
   lhs->ToDenseMatrix(&eigen_lhs);
   EXPECT_NEAR((actual - expected).norm() / actual.norm(),
               0.0,
-              std::numeric_limits<double>::epsilon() * 10)
+              std::numeric_limits<double>::epsilon() * 20)
       << "\n"
       << eigen_lhs;
 }