fix: lock @vue/test-utils version as it's still in beta and may introduce breaking changes

Author: haoqunjiang

packages/@vue/cli-plugin-unit-jest/generator/index.js

@@ -8,7 +8,7 @@ module.exports = (api, _, __, invoking) => {
       'test:unit': 'vue-cli-service test:unit'
     },
     devDependencies: {
-      '@vue/test-utils': '^1.0.0-beta.20'
+      '@vue/test-utils': '1.0.0-beta.29'
     },
     jest: {
       'moduleFileExtensions': [

packages/@vue/cli-plugin-unit-jest/package.json

@@ -32,7 +32,7 @@
     "vue-jest": "^3.0.3"
   },
   "devDependencies": {
-    "@vue/test-utils": "^1.0.0-beta.20",
+    "@vue/test-utils": "1.0.0-beta.29",
     "ts-jest": "^23.0.0"
   }
 }

packages/@vue/cli-plugin-unit-mocha/generator/index.js

@@ -5,7 +5,7 @@ module.exports = (api, _, __, invoking) => {
 
   api.extendPackage({
     devDependencies: {
-      '@vue/test-utils': '^1.0.0-beta.20',
+      '@vue/test-utils': '1.0.0-beta.29',
       'chai': '^4.1.2'
     },
     scripts: {

packages/@vue/cli-plugin-unit-mocha/package.json

@@ -29,7 +29,7 @@
     "mocha-webpack": "^2.0.0-beta.0"
   },
   "devDependencies": {
-    "@vue/test-utils": "^1.0.0-beta.20",
+    "@vue/test-utils": "1.0.0-beta.29",
     "chai": "^4.1.2"
   },
   "publishConfig": {