Building docs: fix positional fetch-license argument

[jpmcb]

Description of changes:

When going through the BUILDING.md docs and attempting to run the fetch-license target, the positonal arg is out of order, causing fetch license task to be skipped:

❯ cargo make fetch-licenses -e BUILDSYS_UPSTREAM_LICENSE_FETCH="true"
[cargo-make] INFO - cargo make 0.35.16
[cargo-make] INFO - Build File: Makefile.toml
[cargo-make] INFO - Task: fetch-licenses
[cargo-make] INFO - Profile: development
[cargo-make] INFO - Running Task: setup
[cargo-make] INFO - Running Task: setup-build
[cargo-make] INFO - Running Task: fetch-sdk
[cargo-make] INFO - Running Task: fetch-toolchain
[cargo-make] INFO - Running Task: fetch-sources
[cargo-make] INFO - Running Task: fetch-vendored
[cargo-make] INFO - Running Task: fetch-licenses
Skipping fetching licenses
[cargo-make] INFO - Build Done in 3.88 seconds.

Here it is working as intended with the right ordering:

❯ cargo make -e BUILDSYS_UPSTREAM_LICENSE_FETCH="true" fetch-licenses
[cargo-make] INFO - cargo make 0.35.16
[cargo-make] INFO - Build File: Makefile.toml
[cargo-make] INFO - Task: fetch-licenses
[cargo-make] INFO - Profile: development
[cargo-make] INFO - Running Task: setup
[cargo-make] INFO - Running Task: setup-build
[cargo-make] INFO - Running Task: fetch-sdk
[cargo-make] INFO - Running Task: fetch-toolchain
[cargo-make] INFO - Running Task: fetch-sources
[cargo-make] INFO - Running Task: fetch-vendored
[cargo-make] INFO - Running Task: fetch-licenses
Skipping copying file from /home/fedora/workspace/bottlerocket-os/bottlerocket/Licenses.toml
[cargo-make] INFO - Build Done in 4.14 seconds.

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.