Support img role for canvas. Fix for #648.

[markwoon]

Tweaking recommendation for no-interactive-element-to-noninteractive-role to support img role on canvas.

Fixes #648.

[ljharb]

LGTM, but want to confirm with @jessebeach first

[codecov]

Codecov Report

Merging #796 (55e5c11) into master (36102cd) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #796   +/-   ##
=======================================
  Coverage   99.24%   99.24%           
=======================================
  Files          98       98           
  Lines        1453     1453           
  Branches      477      477           
=======================================
  Hits         1442     1442           
  Misses         11       11           

Impacted Files	Coverage Δ
src/index.js	100.00% <ø> (ø)

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[jessebeach]

Thanks @markwoon and @ljharb !