removed setting ctrlKey since it's read-only

[joshuagish]

event.ctrlKey is read-only which causes errors in the console when we try to set it

see https://www.w3schools.com/jsref/event_ctrlkey.asp

[coveralls]

Coverage decreased (-0.04%) to 87.898% when pulling 6dc564b on thecitywelivein:master into 91c184a on hyojin:master.

[hyojin]

@thecitywelivein Hi, thanks for your PR. Yes, it's read-only. but it's the way to handle multiple selection in material-ui internally now. Probably it will be disappeared on v1.
By the way, I couldn't get errors on latest chrome and FF. which browsers throw that error?

[coveralls]

Coverage increased (+0.04%) to 87.975% when pulling 5b38d9e on thecitywelivein:master into 91c184a on hyojin:master.

[joshuagish]

Looks like typescript is causing the error to be shown. Wrapping it in a try/catch prevents errors for me. I've updated the PR

This is the error