Fixes the type/format typo for ActivityStats
Fixes the type/format typo for ActivityStats

In https://github.com/strava/developers.strava.com/commit/d8b419097e0d393c723615385743091a927e69b0, I made an attempt to properly declare those fields as floats - but I didn't actually properly follow the OpenAPI spec, which mandates floating point numbers to be declared as `number`s with a `format` of `float`.

Without this change, the Swagger code generator shows a warning but still generates the code.

Additionally, Todd's comment in the previous PR led me to think it'd be better to use double here, so I'm doing that.

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