Fixed clippy warnings in lambda-events

[rimutaka]

A minor fix to remove Clippy warnings in lambda-events:

this expression creates a reference which is immediately dereferenced by the compiler
for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
`#[warn(clippy::needless_borrow)]` on by defaultclippy[Click for full compiler diagnostic](rust-analyzer-diagnostics-view:/diagnostic%20message%20%5B0%5D?0#file%3A%2F%2F%2Fhome%2Fmx%2Fprojects%2Fgh-forks%2Faws-lambda-rust-runtime-fork%2Flambda-events%2Fsrc%2Fevent%2Fcloudwatch_events%2Fcloudtrail.rs)
cloudtrail.rs(103, 59): change this to: `output.as_bytes()`

Weirdly enough, the warnings came up in VSCode, but not in the CLI.
@martinjlowm, please take a look if you get a chance in case I'm breaking something with this fix. It was your code.

🔏 By submitting this pull request

• I confirm that I've ran cargo +nightly fmt.
• I confirm that I've ran cargo clippy --fix.
• I confirm that I've made a best effort attempt to update all relevant documentation.
• I confirm that my contribution is made under the terms of the Apache 2.0 license.

[calavera]

thanks!