Fix conversion error for EMR waiters

Found by someboredkiddo
Introduced in 23e042ff8716003ee53d62698668a95fe318c4b8

Closes #378
Fixes aws/aws-cli#1007
Merge branch 'emr-waiter-config-2' into develop

* emr-waiter-config-2:
  Fix conversion error for EMR waiters