Mismatched CodePipeline CloudWatch fields

Hi all, thanks for your support on this library. I was recently trying to replace our homemade structs for CodePipeline events with the ones defined in this package but I'm running into the following errors unmarshalling the `version` fields in `CodePipelineEventDetail` and `CodePipelineEventDetail`:

```Go
json: cannot unmarshal number 2.0 into Go struct field CodePipelineEventDetail.detail.version of type int64: errorString null

json: cannot unmarshal string into Go struct field CodePipelineEventDetailType.detail.type.version of type int64: errorString null
```

The unmarshalling works when `CodePipelineEventDetail.detail.version` is a `float64` and `CodePipelineEventDetailType.detail.type.version` is a string (using our own structs). Would y'all mind taking another look at the types for the two `versions` fields?

Based on the comments for each of them, it sounds like there's some mismatch in the schema/documentation:
https://github.com/aws/aws-lambda-go/blob/96ab249f3eb7644ebc3bb7a190d268184fdd9f4e/events/codepipeline_cloudwatch.go#L82-L83

https://github.com/aws/aws-lambda-go/blob/96ab249f3eb7644ebc3bb7a190d268184fdd9f4e/events/codepipeline_cloudwatch.go#L105-L106

Thanks!

Start in events/codepipeline_cloudwatch.go at the referenced lines for the CodePipelineEventDetail and CodePipelineEventDetailType version fields. Compare those declarations with the reported JSON unmarshalling errors and the comments, then confirm that representative numeric and string version values decode successfully with the corrected types.

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