[improvement] Toast: optimize image icon display (#3895)

src/image/test/__snapshots__/index.spec.js.snap

@@ -25,6 +25,6 @@ exports[`load event 2`] = `
 </div>
 `;
 
-exports[`loading-placeholder prop 1`] = `<div class="van-image"><img class="van-image__img"></div>`;
+exports[`show-loading prop 1`] = `<div class="van-image"><img class="van-image__img"></div>`;
 
 exports[`show-error prop 1`] = `<div class="van-image"></div>`;

src/image/test/index.spec.js

@@ -102,10 +102,10 @@ test('lazy-load error event', done => {
   });
 });
 
-test('loading-placeholder prop', () => {
+test('show-loading prop', () => {
   const wrapper = mount(Image, {
     propsData: {
-      loadingPlaceholder: false
+      showLoading: false
     }
   });