[gql] `input` type is not getting converted

`input` types in GraphQL are not getting converted.

Example:

```gql
##### type.graphql #####

type Foo {
bar: String!
}

##### input.graphql #####

input FooInput {
bar: String!
}
```

```sh
$ typeconv -f gql -t ts ./type.graphql

💡 Converted 1 types in 1 files, in 0.0s

$ typeconv -f gql -t ts ./input.graphql

💡 Converted 0 types in 1 files, in 0.0s

# Note that I wrote this output myself and didn't actually test the two files above ;-)
# I did test the behavior with actual development/production use GraphQL schmas however
```