Fix sidebar navigation list toggle.

Prettier managled `@include breakpoint` media queries causing the input/checkbox toggle hack styles to go missing.

Fixes mmistakes#1819

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Bug Fixes
 
+* Fix sidebar navigation list toggle. [#1819](https://github.com/mmistakes/minimal-mistakes/issues/1819)
 * Fix hover animation for links with `:visited` state. [#1820](https://github.com/mmistakes/minimal-mistakes/issues/1820)
 
 ## [4.12.2](https://github.com/mmistakes/minimal-mistakes/releases/tag/4.12.2)

_sass/minimal-mistakes/_navigation.scss

@@ -340,7 +340,7 @@
     display: none;
   }
 
-  @include breakpoint(max-width($large - 1px)) {
+  @include breakpoint(max-width $large - 1px) {
     label {
       position: relative;
       display: inline-block;
@@ -446,7 +446,7 @@
     font-weight: bold;
   }
 
-  @include breakpoint(max-width($large - 1px)) {
+  @include breakpoint(max-width $large - 1px) {
     position: relative;
     max-height: 0;
     opacity: 0%;
@@ -460,7 +460,7 @@
   }
 }
 
-@include breakpoint(max-width($large - 1px)) {
+@include breakpoint(max-width $large - 1px) {
   .nav__list input:checked ~ .nav__items {
     -webkit-transition: 0.5s ease-in-out;
     transition: 0.5s ease-in-out;

docs/_docs/18-history.md

@@ -4,14 +4,15 @@ permalink: /docs/history/
 excerpt: "Change log of enhancements and bug fixes made to the theme."
 sidebar:
   nav: docs
-last_modified_at: 2018-09-05T15:18:48-04:00
+last_modified_at: 2018-09-05T15:28:14-04:00
 toc: true
 ---
 
 ## Unreleased
 
 ### Bug Fixes
 
+* Fix sidebar navigation list toggle. [#1819](https://github.com/mmistakes/minimal-mistakes/issues/1819)
 * Fix hover animation for links with `:visited` state. [#1820](https://github.com/mmistakes/minimal-mistakes/issues/1820)
 
 ## [4.12.2](https://github.com/mmistakes/minimal-mistakes/releases/tag/4.12.2)