bugfix:_computedWatchers应该赋值_computedWatcher['value'],不是监听对象本身，否则

会引发循环引用

Author: sexdevil

packages/mpvue/index.js

@@ -5469,7 +5469,7 @@ function diffData (vm, data) {
       data[rootKey + '.' + mpItemKey] = vmMpProps[mpItemKey];
     });
     Object.keys(vmComputedWatchers).forEach(function (computedItemKey) {
-      data[rootKey + '.' + computedItemKey] = vmComputedWatchers[computedItemKey];
+      data[rootKey + '.' + computedItemKey] = vmComputedWatchers[computedItemKey]['value'];
     });
       // 更新的时候要删除$root.0:{},否则会覆盖原正确数据
     delete data[rootKey];

src/platforms/mp/runtime/diff-data.js

@@ -144,7 +144,7 @@ export function diffData (vm, data) {
       data[rootKey + '.' + mpItemKey] = vmMpProps[mpItemKey]
     })
     Object.keys(vmComputedWatchers).forEach((computedItemKey) => {
-      data[rootKey + '.' + computedItemKey] = vmComputedWatchers[computedItemKey]
+      data[rootKey + '.' + computedItemKey] = vmComputedWatchers[computedItemKey]['value']
     })
       // 更新的时候要删除$root.0:{},否则会覆盖原正确数据
     delete data[rootKey]