Fix when running inside venv

[rdb]

Running python inside a venv requires an explicit importlib.machinery import, oddly:

python -m venv env
env/bin/python
>>> import importlib
>>> importlib.machinery
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'importlib' has no attribute 'machinery'
>>> import importlib.machinery
>>> importlib.machinery
<module 'importlib.machinery' from '/usr/local/lib/python3.7/importlib/machinery.py'>

[codecov-commenter]

Codecov Report

Merging #2 into master will decrease coverage by 2.24%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master       #2      +/-   ##
==========================================
- Coverage   56.84%   54.60%   -2.25%     
==========================================
  Files           4        5       +1     
  Lines         146      152       +6     
==========================================
  Hits           83       83              
- Misses         63       69       +6     

Impacted Files	Coverage Δ
limeade/_scan_helpers.py	54.54% <0.00%> (ø)
limeade/__init__.py	0.00% <0.00%> (ø)

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