Use var for Zero Value Structs
When all the fields of a struct are omitted in a declaration, use the var
form to declare the struct.
| Bad | Good |
|---|---|
| ```go user := User{} ``` | ```go var user User ``` |
This differentiates zero valued structs from those with non-zero fields similar to the distinction created for map initialization, and matches how we prefer to declare empty slices.