probot: 401 error after deploying probot to gcf

Bug Report

Current Behavior here is the response error iam getting while calling probot deployed on google cloud functions

HttpError: {
    "message": "Missing 'issuer' claim ('iss') in assertion",
    "documentation_url": "https://developer.github.com/v3"
}
at response.text.then.message(/srv/node_modules / @octokit / rest / lib / request / request.js: 72: 19) at < anonymous > at process._tickDomainCallback(internal / process / next_tick.js: 229: 7)

{
    name: 'HttpError',
    code: 401,
    status: undefined,
    headers: {
        'access-control-allow-origin': '*',
        'access-control-expose-headers': 'ETag, Link, Location, Retry-After, X-GitHub-OTP, X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset, X-OAuth-Scopes, X-Accepted-OAuth-Scopes, X-Poll-Interval, X-GitHub-Media-Type',
        connection: 'close',
        'content-length': '111',
        'content-security-policy': 'default-src \'none\'',
        'content-type': 'application/json; charset=utf-8',
        date: 'Wed, 06 Feb 2019 23:33:54 GMT',
        'referrer-policy': 'origin-when-cross-origin, strict-origin-when-cross-origin',
        server: 'GitHub.com',
        status: '401 Unauthorized',
        'strict-transport-security': 'max-age=31536000; includeSubdomains; preload',
        'x-content-type-options': 'nosniff',
        'x-frame-options': 'deny',
        'x-github-media-type': 'github.machine-man-preview; format=json',
        'x-github-request-id': '5091:6932:789C8B:F29F81:5C5B6EE2',
        'x-xss-protection': '1; mode=block'
    }
}