fix(components): [timeline-item] props validation (#8083)

packages/components/timeline/__tests__/timeline.test.ts

@@ -178,7 +178,7 @@ describe('TimeLine.vue', () => {
         <el-timeline>
           <el-timeline-item
             timestamp="2018-04-11"
-            type="large">
+            size="large">
             Step 1: xxxxxx
           </el-timeline-item>
         </el-timeline>

packages/components/timeline/src/timeline-item.ts

@@ -17,10 +17,12 @@ export const timelineItemProps = buildProps({
   },
   placement: {
     type: String,
+    values: ['top', 'bottom'],
     default: 'bottom',
   },
   type: {
     type: String,
+    values: ['primary', 'success', 'warning', 'danger', 'info'],
     default: '',
   },
   color: {
@@ -29,6 +31,7 @@ export const timelineItemProps = buildProps({
   },
   size: {
     type: String,
+    values: ['normal', 'large'],
     default: 'normal',
   },
   icon: {