feat!: set whitespace: 'condense' for template compiler (#3853)

BREAKING CHANGE:
Detailed explanation: https://github.com/vuejs/vue/issues/9208#issuecomment-450012518

Take the following template as example:
```
<p>
  Welcome to <b>Vue.js</b> <i>world</i>.
  Have fun!
</p>
```

With `preserveWhitespace: false`, it was compiled as:
```
<p> Welcome to <b>Vue.js</b><i>world</i>. Have fun! </p>
```

With `whitespace: 'condense'`, it is now compiled as:
```
<p> Welcome to <b>Vue.js</b> <i>world</i>. Have fun! </p>
```

Note the **inline whitespace between tags** is preserved.

Closes #1020

packages/@vue/cli-service/lib/config/base.js

@@ -86,7 +86,7 @@ module.exports = (api, options) => {
           .loader('vue-loader')
           .options(Object.assign({
             compilerOptions: {
-              preserveWhitespace: false
+              whitespace: 'condense'
             }
           }, vueLoaderCacheConfig))