Check for ELEVENTY_ENV for minifier

[Luke-zhang-04]

package.json command cross-env ELEVENTY_ENV=prod NODE_OPTIONS=--max-old-space-size=4096 eleventy doesn't minify HTML because the config file only checks for NODE_ENV.

Also turned on conservativeCollapse and preserveLineBreaks, which will collapse whitespace to just 1 space or 1 newline instead of removing it entirely. This fixes an issue where mathjax blocks would not have spaces between text.