Using instanceof for external libs(graphql) is dangerous

**Is your feature request related to a problem? Please describe.**

The `graphql` module is extremely popular and used by many and many third party dependencies. While its possible to pin a version, it still exposes 2 versions of itself, a *commonjs* version and a *module* version. This can be an issue for the `instanceof` compares in the graphql-module code such as

```
function isScalarResolver(obj: any): obj is GraphQLScalarType {
return obj instanceof GraphQLScalarType;
}
...
export function isNotSchema(obj: any): obj is T {
return obj instanceof GraphQLSchema === false;
}
```

Are the 2 most dangerous usages. When an instanceof these classes resolve to a different file, wether by module type or module version these will fail to work correctly.

**Describe the solution you'd like**
The graphql library supplies its own isSchema and isScalar utilty functions. Use these instead, under the covers its really doing string manipulation.