[CMake] Minimum Eigen is 3.2.8 since #1434.

scripts/cmake/ExternalProjectEigen.cmake

@@ -5,12 +5,12 @@ if(USE_CONAN)
 endif()
 
 if(OGS_LIB_EIGEN STREQUAL "System")
-    find_package(Eigen3 3.2.5 REQUIRED)
+    find_package(Eigen3 3.2.8 REQUIRED)
     if(NOT EIGEN3_FOUND)
         message(FATAL_ERROR "Aborting CMake because system Eigen was not found!")
     endif()
 elseif(OGS_LIB_EIGEN STREQUAL "Default")
-    find_package(Eigen3 3.2.5)
+    find_package(Eigen3 3.2.8)
 endif()
 
 # First check for system Eigen

scripts/cmake/ThirdPartyLibVersions.cmake

@@ -3,8 +3,8 @@ string(REPLACE "." "_" OGS_BOOST_VERSION_UNDERLINE ${OGS_BOOST_VERSION})
 set(OGS_BOOST_URL "http://opengeosys.s3.amazonaws.com/ogs6-lib-sources/boost_${OGS_BOOST_VERSION_UNDERLINE}.tar.bz2")
 set(OGS_BOOST_MD5 "a744cf167b05d72335f27c88115f211d")
 
-set(OGS_EIGEN_URL "http://opengeosys.s3.amazonaws.com/ogs6-lib-sources/eigen-3.2.5.tar.gz")
-set(OGS_EIGEN_MD5 "8cc513ac6ec687117acadddfcacf551b")
+set(OGS_EIGEN_URL "http://opengeosys.s3.amazonaws.com/ogs6-lib-sources/eigen-3.2.8.tar.gz")
+set(OGS_EIGEN_MD5 "135d8d43aaee5fb54cf5f3e981b1a6db")
 
 set(OGS_VTK_VERSION 6.3.0)
 set(OGS_VTK_URL "http://www.vtk.org/files/release/6.3/VTK-6.3.0.tar.gz")