fix example for reading_temperature.rs

[dnutiu]

I'm new to Rust so sorry if I make mistakes.

It seems like the crate from crates.io is not synced to the Github repo and in order to get the example to compile I had to tweak it, please see the PR.

I also had to use the following line in my Cargo.toml.

bme680 = {git = "https://github.com/marcelbuesing/bme680.git", version = "0.6.0"}