Remove forcing of gt_higher_moments to be linked as a shared library

This can cause linking errors if GenTen was not built as a shared library.  Users should configure with BUILD_SHARED_LIBS=ON if they want shared libraries.

joint_moments/CMakeLists.txt

@@ -3,7 +3,7 @@
 set(joint_moment_headers Genten_HigherMoments.hpp)
 
 ADD_LIBRARY (
-  gt_higher_moments SHARED
+  gt_higher_moments
   ${Genten_SOURCE_DIR}/joint_moments/Genten_HigherMoments.cpp
   ${Genten_SOURCE_DIR}/joint_moments/Genten_ComputePrincipalKurtosisVectors.cpp
   )