Schema generator failed for `/` character into enum

### What happened?
Enum with `/` character failed with error "Expected Name, found " during schema generation.
### What did you expect?
I expect to be able to specify every type of enum data, maybe using an escape character if needed.

### Minimal graphql.schema and models to reproduce
```
enum Season {
S/S
A/W
}

type Product {
name: String!
season: Season
}

type ProductInput {
name: String!
season: Season
}
```

### versions
- `gqlgen v0.11.1`
- `go version go1.14`
- via `go modules`

Thanks

Paolo