fix(list): minification-safe element type comparison

[dan-kwiat]

#492
I didn't have a chance to test this - please do so before merging

[codecov-io]

Codecov Report

Merging #509 into rc0.8.0 will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           rc0.8.0     #509   +/-   ##
========================================
  Coverage    96.62%   96.62%           
========================================
  Files           59       59           
  Lines         1984     1984           
  Branches       235      235           
========================================
  Hits          1917     1917           
  Misses          67       67

Impacted Files	Coverage Δ
packages/list/index.js	89.09% <100%> (ø)	⬆️

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[moog16]

@dan-kwiat I tested this by

1. using master, and adding the edits in this PR.
2. ran npm run build && node scripts/release/cp-pkgs.js
3. copied the /List/dist/index.js file to your <https://github.com/dan-kwiat/material-next-template>node_modules/@material/react-list/dist/index.js file
4. I ran yarn export from your material-next-template
5. replaced all instances of /material-next-template/ in the index.html
6. opened index.html

IT WORKED! Thanks again

[moog16]

TESTS: #511

[moog16]

@dan-kwiat while we wait for tests please sign the PR by commenting "I signed it"

[moog16]

@dan-kwiat can you please add the line found in d7981e2

[dan-kwiat]

I signed it