Add missing license to executor

[adriangonz]

What this PR does / why we need it:
Add missing license to executor to fix licenses linter.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[seldondev]

Thu Jul 16 16:51:10 UTC 2020
The logs for [pr-build] [1] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-2147/1.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2147 --build=1

[seldondev]

Thu Jul 16 16:51:33 UTC 2020
The logs for [lint] [2] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-2147/2.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2147 --build=2

[axsaucedo]

lint passes
/approve

[seldondev]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: axsaucedo

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