Set window to dummy object if not defined

[bakkdoor]

This fixes an error when using elm-ui with rtfeldman/elm-css.
Similar to e778f0a

[bakkdoor]

A 1.2.2 release upon merge would be appreciated :)
Related to #77

[bakkdoor]

I ran into this after trying to use the Ui.Input component.

[bakkdoor]

Not sure what the best way is to fix that CI failure. Looks like it can't find XMLHttpRequest now for some reason 😞

[fosskers]

This happens when importing certain modules, but not all. I use emacs's elm-mode, and importing Chooser or NotificationCenter gives me:

> import Day1 exposing (..)
/home/colin/code/horizon/aafa/ui/repl-temp-000.js:5916
    var styles = window.getComputedStyle(document.documentElement, '');
                 ^

ReferenceError: window is not defined
    at /home/colin/code/horizon/aafa/ui/repl-temp-000.js:5916:18
    at Object.<anonymous> (/home/colin/code/horizon/aafa/ui/repl-temp-000.js:5924:2)
    at Object.<anonymous> (/home/colin/code/horizon/aafa/ui/repl-temp-000.js:15243:4)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)
    at Module.runMain (module.js:605:10)
    at run (bootstrap_node.js:423:7)

when I try to recompile my code in my embedded repl.

[gdotdesign]

This commit f983acf should fix the original issue, I'm not sure if would fix elm-mode errors.