Fix new flake8 errors

[rly]

Fix #350

[codecov]

Codecov Report

Merging #351 into dev will not change coverage.
The diff coverage is 61.11%.

@@           Coverage Diff           @@
##              dev     #351   +/-   ##
=======================================
  Coverage   73.51%   73.51%           
=======================================
  Files          33       33           
  Lines        6535     6535           
  Branches     1424     1424           
=======================================
  Hits         4804     4804           
  Misses       1306     1306           
  Partials      425      425           

Impacted Files	Coverage Δ
src/hdmf/common/table.py	69.50% <0.00%> (ø)
src/hdmf/backends/hdf5/h5tools.py	66.49% <50.00%> (ø)
src/hdmf/container.py	72.75% <60.00%> (ø)
src/hdmf/build/builders.py	86.68% <66.66%> (ø)
src/hdmf/backends/hdf5/h5_utils.py	66.42% <100.00%> (ø)

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[ajtritt]

@rly I addressed these in #346. Closing to avoid merge conflicts