Docs Minor Change: Fuelup Installation Guide

## Expected Behavior
Currently the docs link - [Fuelup check toolchain](https://docs.fuel.network/guides/installation/#checking-your-current-toolchain) on running the `fuelup show` command gives output which mentions `beta-4-x86_64-unknown-linux-gnu (default)` as the active toolchain.

But the last line in the docs mention - `As you can see, the beta-5 toolchain is active 🚀`. This might be confusing to devs looking to setup fuel.

## Actual Behavior
Replace the actual output with the right output (beta-5)