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!

CodePipelineEventDetail と CodePipelineEventDetailType の version フィールドについて、参照されている行の events/codepipeline_cloudwatch.go から始めます。これらの宣言を報告されている JSON unmarshalling エラーおよびコメントと比較し、その後、version の代表的な数値および文字列の値が、修正後の型で正常にデコードされることを確認します。

索引モデルが issue の本文から書いたものです。