add user agent to coingecko api call

[Alesfatalis]

Fixes error

{
    "status": {
        "error_code": 403,
        "error_message": "Please add a descriptive User-Agent to your request. For higher rate limits & stable integration, please subscribe to our API plans: https://www.coingecko.com/en/api/pricing . If you think this is a mistake, please report here: https://forms.gle/3V2z8Mb3k2RMu5S2A"
    }
}

[coveralls]

Pull Request Test Coverage Report for Build 20847856951

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.7%) to 52.477%

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Totals
Change from base Build 18064399903:	-0.7%
Covered Lines:	1928
Relevant Lines:	3674

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💛 - Coveralls