remove only one key initialization condition

[timofey97]

We have a need to work with different stripe accounts in one application. With each payment, we change and initialize different public keys from different companies. But initialization worked painlessly only on ios, on android we found a small flaw in the plugin code.
If you remove the check for an empty publishableKey, then everything works as it should)

If possible, please add this to the update or if you have any ideas on how to improve and secure the code, I will be glad to any suggestions

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[rdlabo]

Thanks pull request. We did not consider that kind of usage. Thanks for your contribution!

[rdlabo]

@timofey97 Did you use this plugin for production? If yes, please tell us what app. This help development this plugin.

👉 #145

Thanks.