* adds !default declarations to a11y variables (#1032)

Merged in after double-checking a11y.scss won't get overwritten by `grunt lessToSass`. Thank you, Claas!

themes/bootstrap3/scss/vendor/a11y.scss

@@ -59,58 +59,58 @@ input, textarea {
 // Navbar
 // -------------------------
 
-$navbar-default-color:             #fff;
-$navbar-default-bg:                #132531;
-$navbar-default-border:            darken($navbar-default-bg, 6.5%);
+$navbar-default-color:             #fff !default;
+$navbar-default-bg:                #132531 !default;
+$navbar-default-border:            darken($navbar-default-bg, 6.5%) !default;
 
 // Navbar links
-$navbar-default-link-color:                #fff;
-$navbar-default-link-hover-color:          #132531;
-$navbar-default-link-hover-bg:             #fff;
-$navbar-default-link-active-color:         #132531;
-$navbar-default-link-active-bg:            #fff;
-$navbar-default-link-disabled-color:       #fff;
-$navbar-default-link-disabled-bg:          #068139;
+$navbar-default-link-color:                #fff !default;
+$navbar-default-link-hover-color:          #132531 !default;
+$navbar-default-link-hover-bg:             #fff !default;
+$navbar-default-link-active-color:         #132531 !default;
+$navbar-default-link-active-bg:            #fff !default;
+$navbar-default-link-disabled-color:       #fff !default;
+$navbar-default-link-disabled-bg:          #068139 !default;
 
 // Navbar brand label
-$navbar-default-brand-color:               $navbar-default-link-color;
-$navbar-default-brand-hover-color:         #068139; //contrast 3.15, so min 19px;
+$navbar-default-brand-color:               $navbar-default-link-color !default;
+$navbar-default-brand-hover-color:         #068139 !default; //contrast 3.15, so min 19px;
 .navbar-brand {
   font-size: 20px;
 }
-$navbar-default-brand-hover-bg:            transparent;
+$navbar-default-brand-hover-bg:            transparent !default;
 
 // Navbar toggle
-$navbar-default-toggle-hover-bg:           #ddd;
-$navbar-default-toggle-icon-bar-bg:        #888;
-$navbar-default-toggle-border-color:       #ddd;
+$navbar-default-toggle-hover-bg:           #ddd !default;
+$navbar-default-toggle-icon-bar-bg:        #888 !default;
+$navbar-default-toggle-border-color:       #ddd !default;
 
-$brand-primary:         #265680;
-$brand-success:         #028302;
-$brand-info:            #1C5F74;
-$brand-warning:         #A56100;
-$brand-danger:          #A41915;
+$brand-primary:         #265680 !default;
+$brand-success:         #028302 !default;
+$brand-info:            #1C5F74 !default;
+$brand-warning:         #A56100 !default;
+$brand-danger:          #A41915 !default;
 
 /* buttons */
-$btn-primary-color:              #fff;
-$btn-primary-bg:                 $brand-primary;
-$btn-primary-border:             #fff;
+$btn-primary-color:              #fff !default;
+$btn-primary-bg:                 $brand-primary !default;
+$btn-primary-border:             #fff !default;
 
-$btn-success-color:              #fff;
-$btn-success-bg:                 $brand-success;
-$btn-success-border:             #fff;
+$btn-success-color:              #fff !default;
+$btn-success-bg:                 $brand-success !default;
+$btn-success-border:             #fff !default;
 
-$btn-info-color:              #fff;
-$btn-info-bg:                 $brand-info;
-$btn-info-border:             #fff;
+$btn-info-color:              #fff !default;
+$btn-info-bg:                 $brand-info !default;
+$btn-info-border:             #fff !default;
 
-$btn-warning-color:              #fff;
-$btn-warning-bg:                 $brand-warning;
-$btn-warning-border:             #fff;
+$btn-warning-color:              #fff !default;
+$btn-warning-bg:                 $brand-warning !default;
+$btn-warning-border:             #fff !default;
 
-$btn-danger-color:              #fff;
-$btn-danger-bg:                 $brand-danger;
-$btn-danger-border:             #fff;
+$btn-danger-color:              #fff !default;
+$btn-danger-bg:                 $brand-danger !default;
+$btn-danger-border:             #fff !default;
 
 
 /* link on white background */