When creating a model with a custom table name (through Config) that is the singular form of the model name, generated migration code cycles between dropping and creating the index.
To generate the migration code, run migrate.go, which will produce the migration.sql file. The first time it's run, replace the $1 with the correct table name.
After migrating the database, run migrate.go again. This will overwrite migration.sql and produce a file that contains a line to drop the index.
After dropping the index, run migrate.go again. The new migration.sql file will contain a line to create the index again the same as it did initially.
After this the cycle repeats.
Try removing the Config method on the Employee model, the migration cycle behavior goes away.
Try using a different table name (other than "employee", e.g. "emp"), the migration cycle behavior goes away.