修复Grid栅格组件Col属性xl和xxl无效的问题

src/components/grid/col.vue

@@ -19,7 +19,9 @@
             xs: [Number, Object],
             sm: [Number, Object],
             md: [Number, Object],
-            lg: [Number, Object]
+            lg: [Number, Object],
+            xl: [Number, Object],
+            xxl: [Number, Object]
         },
         data () {
             return {
@@ -40,7 +42,7 @@
                     }
                 ];
 
-                ['xs', 'sm', 'md', 'lg'].forEach(size => {
+                ['xs', 'sm', 'md', 'lg', 'xl', 'xxl'].forEach(size => {
                     if (typeof this[size] === 'number') {
                         classList.push(`${prefixCls}-span-${size}-${this[size]}`);
                     } else if (typeof this[size] === 'object') {

src/styles/common/layout.less

@@ -81,8 +81,26 @@
 
 // Large grid
 //
-// Columns, offsets, pushes, and pulls for the large desktop device range.
+// Columns, offsets, pushes, and pulls for the wide desktop device range.
 
 @media (min-width: @screen-lg-min) {
     .make-grid(-lg);
 }
+
+
+// Extra large grid
+//
+// Columns, offsets, pushes, and pulls for the full hd desktop device range.
+
+@media (min-width: @screen-xl-min) {
+    .make-grid(-xl);
+}
+
+
+// Extra extra large grid
+//
+// Columns, offsets, pushes, and pulls for the large desktop device range.
+
+@media (min-width: @screen-xxl-min) {
+    .make-grid(-xxl);
+}