Susy Error: WARNING: Static math requires a valid column-width setting

Question

I continue to get this error in my terminal.

Error: WARNING: Static math requires a valid column-width setting

I am currently using gulp and gulp-sass for my app. This is my main.scss file, and I can't seem to figure out how to satisfy this error. The actual error brings up nothing in Google, and I have followed Susy's docs. Susy also states that I don't need Compass, so I haven't installed gulp-compass.

main.scss

@import "susy";

$susy: (
  columns: 12,
  gutters: 1/4,
  math: fluid,
  output: float,
  container: 1140px,
  gutter-position: inside,
);

#main {
  @include container;
}

gulpfile.js

gulp.task('css', function () {
  gulp.src('./src/scss/main.scss')
    .pipe(sourcemaps.init())
    .pipe(sass({
      errLogToConsole: true,
      sourceComment: 'normal'
    } ))
    .pipe(sourcemaps.write())
    .pipe(gulp.dest('./dist'));
});