Add new line to code nav popover

It improves the view of multiline structures:

Before:

```go
struct { httpClient *HttpClient user string password
string secret string userAgent string }
```

After:

```go
struct {
httpClient *HttpClient
user string
password string
secret string
userAgent string
}
```

Changelog: fixed

app/assets/javascripts/code_navigation/components/doc_line.vue

@@ -18,5 +18,6 @@ export default {
     <span v-for="(token, tokenIndex) in tokens" :key="tokenIndex" :class="token.class">{{
       token.value
     }}</span>
+    <br />
   </span>
 </template>