yum update seemingly not needed for operator

[ryandawsonuk]

realised yum isn't available in the go base image... think we don't need to run it for that one... so fixing mistake from #2870

seldon-core/jenkins-x/logs/SeldonIO/seldon-core/v1.6.0-release/5.log

Line 4211 in bc1c069

The command '/bin/sh -c yum -y update-minimal --security --sec-severity=Important --sec-severity=Critical' returned a non-zero code: 127

[seldondev]

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