Update to NEST 3.0

use a recent version of NEST

load_sim_tools.sh

@@ -21,7 +21,7 @@ spack load -r py-numpy %gcc@10.3.0
 spack load -r py-pip %gcc@10.3.0
 spack load -r arbor %gcc@10.3.0
 spack load -r neuron %gcc@10.3.0
-spack load -r nest@2.20.0 %gcc@10.3.0
+spack load -r nest@3.0 %gcc@10.3.0
 spack load -r py-pynn %gcc@10.3.0
 
 echo "Everything ready!"