title: Error while converting Bootstrap-Sass with gulp, but other sass files work
body: <p>Trying to convert bootstrap-sass to css using gulp. Here's my gulpfile</p>
  
  <pre><code>var gulp = require('gulp');
  var sass = require('gulp-ruby-sass');
  
  // Concatenate Sass
  gulp.task('sass', function() {
    var sassFiles = 'bower_components/bootstrap-sass/assets/stylesheets/_bootstrap.scss'
    return sass(sassFiles, {style: 'compressed', emitCompileError: true})
      .pipe(gulp.dest(dest + 'scss'));
  });
  
  // Default Task
  gulp.task('default', ['sass']);
  </code></pre>
  
  <p>This throws the following error:</p>
  
  <pre><code>[12:18:42] Starting 'sass'...
  [12:18:45] What files should I watch? Did you mean something like:
      sass --watch input.sass:output.css
      sass --watch input-dir:output-dir
    Use --trace for backtrace.
  
  events.js:72
          throw er; // Unhandled 'error' event
                ^
  Error: Sass compilation failed. See console output for more information.
  </code></pre>
  
  <p>However, if I use my own sass files instead of bootstrap-sass it works fine and converts my sass to css as expected. What am I missing?</p>