Add JEKYLL_ENV=production to Gulp's build task

[eksperimental]

Fixes https://github.com/core77/jekyll-foundation/pull/40#issuecomment-264845968

[core77]

I'm wondering in the jekyll config you check if the environment is 'development' (to ignore the compress.html layout).

In the jekyll gulp task you set 'production'.

Where ist the 'development' environment beeing set?

[eksperimental]

according to Jekyll documentation, 'development' is the default environment

[eksperimental]

another way of doing this is to define the ENV in package.json

  "scripts": {
    "start": "gulp",
    "build": "JEKYLL_ENV=production gulp build --production",
    "test": "JEKYLL_ENV=production gulp build --production"
  },

but doing it inside gulp allows us to call gulp directly

[core77]

👍