Replacing breakpoint-sass module with custom mixin.

sass/init/breakpoint/_respond-to.scss

@@ -0,0 +1,9 @@
+@mixin respond-to($breakpoint) {
+  // If the key exists in the map
+  @if map-has-key($breakpoints, $breakpoint) {
+    // Prints a media query based on the value
+    @media (min-width: map-get($breakpoints, $breakpoint)) {
+      @content;
+    }
+  }
+}