chore(millercolumns): rename custom properties

Author: jenndiaz

components/miller/index.css

@@ -11,31 +11,31 @@ governing permissions and limitations under the License.
 */
 
 .spectrum-MillerColumns {
-  --spectrum-millercolumn-inline-size: 272px;
-  --spectrum-millercolumn-padding: var(--spectrum-spacing-100);
-  --spectrum-millercolumn-margin-left: var(--spectrum-spacing-100);
-  --spectrum-millercolumn-margin-right: var(--spectrum-spacing-100);
+  --spectrum-millercolumns-inline-size: 272px;
+  --spectrum-millercolumns-padding: var(--spectrum-spacing-100);
+  --spectrum-millercolumns-margin-inline-start: var(--spectrum-spacing-100);
+  --spectrum-millercolumns-margin-inline-end: var(--spectrum-spacing-100);
 }
 
 .spectrum-MillerColumns {
   overflow-x: auto;
   white-space: nowrap;
   user-select: none;
-  padding: var(--mod-millercolumn-padding, var(--spectrum-millercolumn-padding)) 0;
+  padding: var(--mod-millercolumns-padding, var(--spectrum-millercolumns-padding)) 0;
 }
 
 .spectrum-MillerColumns-item {
   display: inline-block;
-  inline-size: var(--mod-millercolumn-inline-size, var(--spectrum-millercolumn-inline-size));
+  inline-size: var(--mod-millercolumns-inline-size, var(--spectrum-millercolumns-inline-size));
   vertical-align: top;
   outline: none;
   margin: 0;
   padding: 0;
-  margin-inline-end: var(--mod-millercolumn-margin-right, var(--spectrum-millercolumn-margin-right));
+  margin-inline-end: var(--mod-millercolumns-margin-inline-end, var(--spectrum-millercolumns-margin-inline-end));
   overflow: auto;
   block-size: 100%;
 
   &:first-child {
-    margin-inline-start: var(--mod-millercolumn-margin-left, var(--spectrum-millercolumn-margin-left));
+    margin-inline-start: var(--mod-millercolumns-margin-inline-start, var(--spectrum-millercolumns-margin-inline-start));
   }
 }