Fix CronJob manifest verification

[rndstr]

This fixes the error

verifying changes: failed to verify changes: updating container
\"some-cronjob\" in resource \"default:cronjob/some-cronjob\" failed:
container \"some-cronjob\" not found in workload

while verifying a CronJob file.

yaml.Unmarshal unmarshals from yaml fields into struct fields
according to their lowercase version. For the struct field JobTemplate
it is looking for jobtemplate while it is actually named
jobTemplate.

Fixes #1126

[squaremo]

Nice catch, thanks @rndstr 🥇