Fixed a typo in the exception block in update_fields method.

https://bugzilla.redhat.com/show_bug.cgi?id=1148518
https://bugzilla.redhat.com/show_bug.cgi?id=1148519
Merge pull request #751 from h-kataria/fixed_typo_in_automate_schema_field_editor

Fixed a typo in the exception block in update_fields method.