Added fix for the import docs

[SachinBahukhandi]

Under the section: https://github.com/firebase/php-jwt#exception-handling

try {
    $decoded = JWT::decode($payload, $keys);
} catch (LogicException $e) {
    // errors having to do with environmental setup or malformed JWT Keys
} catch (UnexpectedValueException $e) {
    // errors having to do with JWT signature and claims
}

Added imports to this section.

[google-cla]

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[bshaffer]

This looks great but please sign the CLA!

[SachinBahukhandi]

This looks great but please sign the CLA!

I had already done it, and forgot to perform a re-scan. Could you please check now?