Fix xeus jupyter kernel linking error.

Author: kpeeters

client_server/CMakeLists.txt

@@ -60,6 +60,7 @@ set(JUPYTER_KERNEL_SRC
     Server.cc
     ${CADABRA_CORE_DIR}/InstallPrefix.cc
     ${CADABRA_CORE_DIR}/DataCell.cc
+    ${CADABRA_CORE_DIR}/Exceptions.cc 
     ${CADABRA_CORE_DIR}/CdbPython.cc 
     ${CADABRA_CORE_DIR}/Stopwatch.cc 
     ${CADABRA_LIBS_DIR}/whereami/whereami.c

cmake/version.cmake

@@ -1,7 +1,7 @@
 set(CADABRA_VERSION_MAJOR 2)
 set(CADABRA_VERSION_MINOR 3)
 set(CADABRA_VERSION_PATCH 6)
-set(CADABRA_VERSION_TWEAK 1)
+set(CADABRA_VERSION_TWEAK 2)
 set(COPYRIGHT_YEARS "2001-2020")
 math(EXPR SYSTEM_BITS "${CMAKE_SIZEOF_VOID_P} * 8")
 find_program(GIT git PATHS ${GIT_DIR})