restore physics dependencies in the environment

science/environment.yml

@@ -3,6 +3,10 @@ dependencies:
   # misc tools
   - conda-forge::nbdime=1.0.6
 
+  # main physics packages
+  - conda-forge::kwant=1.4.1
+  - conda-forge::sympy=1.4.0
+
   # main scientific packages
   - conda-forge::scipy=1.3.0
   - conda-forge::numpy=1.16.4