Fix Sass compile error by importing mixins (#308)

Author: DiogoRibeiro7

_sass/minimal-mistakes/_base.scss

@@ -4,6 +4,7 @@
 
 @use "variables" as *;
 @use "vendor/breakpoint/breakpoint" as *;
+@use "mixins";
 
 html {
   /* sticky footer fix */

_sass/minimal-mistakes/_reset.scss

@@ -4,6 +4,7 @@
 
 @use "variables" as *;
 @use "vendor/breakpoint/breakpoint" as *;
+@use "mixins";
 
 * { box-sizing: border-box; }