feat(typescript): make typescript a peer dep so user can specify its version

Author: yyx990803

packages/@vue/cli-plugin-typescript/generator/index.js

@@ -7,6 +7,12 @@ module.exports = (api, {
     lintOn = lintOn.split(',')
   }
 
+  api.extendPackage({
+    devDependencies: {
+      typescript: '^2.9.0'
+    }
+  })
+
   if (classComponent) {
     api.extendPackage({
       dependencies: {

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

@@ -27,8 +27,10 @@
     "fork-ts-checker-webpack-plugin": "^0.4.3",
     "globby": "^8.0.1",
     "ts-loader": "^4.4.2",
-    "tslint": "^5.10.0",
-    "typescript": "~2.9.0"
+    "tslint": "^5.10.0"
+  },
+  "peerDependencies": {
+    "typescript": ">=2"
   },
   "devDependencies": {
     "@types/chai": "^4.1.0",