snap: Skip installing postcss due to failure on build server
snap: Skip installing postcss due to failure on build server

npm running on fails to fetch postcss-cli on build.snapcraft.io
due to network proxy issue.

See https://forum.snapcraft.io/t/build-fails-behind-proxy-on-build-snapcraft-io/6951/3

gohugoio/hugo,mdhender/hugo,anthonyfok/hugo,fedelibre/hugo,fedelibre/hugo,mdhender/hugo,mdhender/hugo,mdhender/hugo,fedelibre/hugo,anthonyfok/hugo,fedelibre/hugo,gohugoio/hugo,gohugoio/hugo,anthonyfok/hugo