Update eslint-plugin-jsx-a11y version

[AlmeroSteyn]

Updated the version of eslint-plugin-jsx-a11y from 6.1.1 to 6.1.2.

Properly closes #4141

Adds clearer error messages for the anchor-is-valid rule as per https://github.com/evcohen/eslint-plugin-jsx-a11y/pull/486.

[AlmeroSteyn]

Ok, I came back later and saw that the Travis build had failed. I tried to run tests locally but, as indicated in the docs, this take a bit more effort on Windows. Locally my tests then seem to fail on some snapshot test error. I think this totally unrelated and has something to do with my enviroment.

Will need to check this out, but I'm out of time for the weekend. Unless someone can check if this is related to upgrading the one package or something else. Or if someone can point me in the right direction as to why this is failing.

I see the following but not the reason why it failed:

e2e-installs.sh: ERROR! An error was encountered executing line 47.
Cleaning up.
yarn config v1.13.0-20181006.0202
success Set "registry" to "https://registry.yarnpkg.com".
Exiting with error.
The command "if [ $TEST_SUITE = "installs" ]; then tasks/e2e-installs.sh; fi" exited with 1.
0.00s$ if [ $TEST_SUITE = "kitchensink" ]; then tasks/e2e-kitchensink.sh; fi

[bugzpodder]

test is sometimes flaky, try retriggering the CI by adding a few no-ops (like a blank line).

[Timer]

Thanks!