Fix Complexity case selection

Use GraphQL field name rather than the Go field name.

codegen/generated!.gotpl

@@ -86,7 +86,7 @@ func (e *executableSchema) Complexity(typeName, field string, childComplexity in
 		{{ if not $object.IsReserved }}
 			{{ range $field := $object.UniqueFields }}
 				{{ if not $field.IsReserved }}
-					case "{{$object.Name}}.{{$field.GoFieldName}}":
+					case "{{$object.Name}}.{{$field.Name}}":
 						if e.complexity.{{$object.Name|go}}.{{$field.GoFieldName}} == nil {
 							break
 						}