title: Incompatible units: 'rem' and 'px' - Bootstrap 4 and Laravel Mix
body: <p>I just installed a fresh Laravel 5.4, and bootstrap 4 alpha 6. Laravel mix wont compile SASS:
  Here is one error:</p>
  
  <pre><code>    Module build failed: ModuleBuildError: Module build failed: 
  $input-height:                   (($font-size-base * $input-line-height) + ($input-padding-y * 2)) !default;
                                  ^
        Incompatible units: 'rem' and 'px'.
        in /Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/bootstrap/scss/_variables.scss (line 444, column 34)
      at runLoaders (/Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/webpack/lib/NormalModule.js:192:19)
      at /Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/loader-runner/lib/LoaderRunner.js:364:11
      at /Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/loader-runner/lib/LoaderRunner.js:230:18
      at context.callback (/Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/loader-runner/lib/LoaderRunner.js:111:13)
      at Object.asyncSassJobQueue.push [as callback] (/Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/sass-loader/lib/loader.js:57:13)
      at Object.&lt;anonymous&gt; (/Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/sass-loader/node_modules/async/dist/async.js:2262:31)
      at apply (/Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/sass-loader/node_modules/async/dist/async.js:20:25)
      at Object.&lt;anonymous&gt; (/Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/sass-loader/node_modules/async/dist/async.js:56:12)
      at Object.callback (/Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/sass-loader/node_modules/async/dist/async.js:944:16)
      at options.error (/Volumes/HDD/nicolae/Dev/htdocs/test/node_modules/node-sass/lib/index.js:294:32)
  
   @ multi ./resources/assets/js/app.js ./resources/assets/sass/app.scss
  </code></pre>
  
  <p>Someone passed this? And how?</p>