typo: Span events: `even` > `event`

Typo on https://agardnerit.github.io/tracepusher/reference/span-events/ even should be `event

tracepusher/docs/reference/span-events.md

Line 23 in 73025fc

    
           For example, to push an event that should be denoted at 100 milliseconds _after_ the span start time, where the event name is `eventA`, the key is `feature_flag.key`, the value is `hexColor` and the even value type (implied) is `stringValue`:

Thanks for taking this on @viktoriussuwandi . Closing as the PR is merged.