Upgrade Hugo to 0.154.3

[chalin]

• Contributes to MacOS installs of Hugo need to be handled differently as of 0.153.0 #2429, hopefully solving it.
• I'm still seeing some strange behavior under macOS, that I resolve by manually "re-" installing cross-env. Seems to be gone after doing a really clean build.
• Submitting this now to confirm whether the CI tests will still pass.

The changes to the generated site files seem to be due to:

• Chroma upgrade: empty spans have been removed, and the light style tweaked
• Image fingerprinting

$ (cd public && git diff -bw --ignore-blank-lines -I 'class="(cl|cp|gi|k|nn|nt)"' -I '_hu_' -I 'Hugo 0.15' -- ':(exclude)*.xml') | grep ^diff | grep -v \.jpg
diff --git a/scss/main.css b/scss/main.css
diff --git a/scss/main.css.map b/scss/main.css.map