ci: fix ts dev dep

Author: yyx990803

packages/@vue/cli-plugin-typescript/package.json

@@ -36,6 +36,7 @@
     "@types/chai": "^4.1.0",
     "@types/jest": "^23.1.4",
     "@types/mocha": "^5.2.4",
+    "typescript": "^2.9.2",
     "vue-class-component": "^6.2.0",
     "vue-property-decorator": "^7.0.0"
   }

yarn.lock

@@ -12060,7 +12060,7 @@ typescript-eslint-parser@^16.0.0:
     lodash.unescape "4.0.1"
     semver "5.5.0"
 
-typescript@~2.9.0:
+typescript@^2.9.2:
   version "2.9.2"
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.9.2.tgz#1cbf61d05d6b96269244eb6a3bce4bd914e0f00c"