Update Library

[NaveenDevrani]

please update the library for android
google play store showing warning
like
"We've detected this app uses an unsupported version of Play billing. Please upgrade to Billing Library version 3 or newer to publish this app."

i also attached the screenshot for your reference
please check and update the billing library

[lilmnm-kamikaze-]

duplicate of issue #486, #490, #478, #477, #458

work is being done in #492.

To make life easier on developers in the future be sure to search the issues and pull requests for the issue you are facing. 9 times out of 10 its already been discussed, with a pull request or commit/release coming.

[serggl]

Upgraded. See #497