Fix "Invalid value for versionCodes: [XXX]"

[NilLlisterri]

The version code was being sent as an array inside an array, raising the following error:
<HttpError 400 when requesting https://www.googleapis.com/androidpublisher/v3/applications/com.xxx.xxx/edits/xxx/tracks/beta?alt=json returned "Invalid value for versionCodes: [100921]">.
Removed the extra square brackets.

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[NilLlisterri]

Just signed it :D

[googlebot]

CLAs look good, thanks!

[nlativy]

Thanks for fixing this!