Consistently use quotes to include Eigen

This makes these files match the convention in the rest of the codebase.

Change-Id: I3a0634274e0e604c575dd3c78fa87f485770e7ff

examples/nist.cc

diff --git a/examples/nist.cc b/examples/nist.cc
index 5bd1003..8ce7291 100644
--- a/examples/nist.cc
+++ b/examples/nist.cc
@@ -71,11 +71,11 @@
 // Average LRE     2.3      4.3       4.0  6.8      4.4    9.4
 //      Winner       0        0         5   11        2     41
 
-#include <Eigen/Core>
 #include <fstream>
 #include <iostream>
 #include <iterator>
 
+#include "Eigen/Core"
 #include "ceres/ceres.h"
 #include "ceres/tiny_solver.h"
 #include "ceres/tiny_solver_cost_function_adapter.h"

include/ceres/tiny_solver_autodiff_function.h

diff --git a/include/ceres/tiny_solver_autodiff_function.h b/include/ceres/tiny_solver_autodiff_function.h
index 0e91142..6bdb2ac 100644
--- a/include/ceres/tiny_solver_autodiff_function.h
+++ b/include/ceres/tiny_solver_autodiff_function.h
@@ -35,7 +35,7 @@
 #ifndef CERES_PUBLIC_TINY_SOLVER_AUTODIFF_FUNCTION_H_
 #define CERES_PUBLIC_TINY_SOLVER_AUTODIFF_FUNCTION_H_
 
-#include <Eigen/Core>
+#include "Eigen/Core"
 
 #include "ceres/jet.h"
 #include "ceres/types.h"  // For kImpossibleValue.

include/ceres/tiny_solver_cost_function_adapter.h

diff --git a/include/ceres/tiny_solver_cost_function_adapter.h b/include/ceres/tiny_solver_cost_function_adapter.h
index d8599e4..e3217d0 100644
--- a/include/ceres/tiny_solver_cost_function_adapter.h
+++ b/include/ceres/tiny_solver_cost_function_adapter.h
@@ -32,7 +32,7 @@
 #ifndef CERES_PUBLIC_TINY_SOLVER_COST_FUNCTION_ADAPTER_H_
 #define CERES_PUBLIC_TINY_SOLVER_COST_FUNCTION_ADAPTER_H_
 
-#include <Eigen/Core>
+#include "Eigen/Core"
 #include "ceres/cost_function.h"
 #include "glog/logging.h"