Enums with trailing white space cause error.

If the enum is `"aborted "` this will cause an error. `"aborted"` is the accepted value. Would like to enhance so that trailing white spaces are allowed, if possible.

When calling the ` schema, err := graphql.NewSchema(schemaConfig)` enums that have a trailing white space cause error.
```bash
Names must match /^[_a-zA-Z][_a-zA-Z0-9]*$/ but "aborted " does not.
```