Fix: migrating config not compatible with camel case props and events (#15260)

src/mixins/migrating.js

+import { kebabCase } from 'element-ui/src/utils/util';
 /**
  * Show migrating guide in browser console.
  *
@@ -29,13 +30,15 @@ export default {
     const definedEvents = componentOptions.listeners || {};
 
     for (let propName in definedProps) {
-      if (definedProps.hasOwnProperty(propName) && props[propName]) {
+      propName = kebabCase(propName); // compatible with camel case
+      if (props[propName]) {
         console.warn(`[Element Migrating][${this.$options.name}][Attribute]: ${props[propName]}`);
       }
     }
 
     for (let eventName in definedEvents) {
-      if (definedEvents.hasOwnProperty(eventName) && events[eventName]) {
+      eventName = kebabCase(eventName); // compatible with camel case
+      if (events[eventName]) {
         console.warn(`[Element Migrating][${this.$options.name}][Event]: ${events[eventName]}`);
       }
     }

src/utils/util.js

@@ -135,3 +135,11 @@ export const autoprefixer = function(style) {
   });
   return style;
 };
+
+export const kebabCase = function(str) {
+  const hyphenateRE = /([^-])([A-Z])/g;
+  return str
+    .replace(hyphenateRE, '$1-$2')
+    .replace(hyphenateRE, '$1-$2')
+    .toLowerCase();
+};