Find out why this plugin doesn't work in Docker

There is probably something wrong with the docker container, but this happened when trying to enable the plugin.

!repos install https://github.com/unitycoders/errbot-calc.git
Installing https://github.com/unitycoders/errbot-calc.git...
Some plugins are generating errors:
  File "/usr/local/lib/python3.6/site-packages/yapsy/PluginManager.py", line 488, in loadPlugins
    candidate_module = imp.load_module(plugin_module_name,plugin_file,candidate_filepath+".py",("py","r",imp.PY_SOURCE))
  File "/usr/local/lib/python3.6/imp.py", line 235, in load_module
    return load_source(name, filename, file)
  File "/usr/local/lib/python3.6/imp.py", line 172, in load_source
    module = _load(spec)
  File "<frozen importlib._bootstrap>", line 684, in
_load
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/errbot/bot/log/plugins/unitycoders/errbot-calc/calc.py", line 16, in <module>
    from sympy import sympify, SympifyError
Plugins reloaded.