Fix permission typo in the e2e-mnist example

[Tomcli]

Which issue is resolved by this Pull Request:
Resolves #

Description of your changes:
The single user default service account is pipeline-runner, so fixing the typo in this example.

Environment tested:

• Python Version (use python --version): 3.7
• Tekton Version (use tkn version): 1.14
• Kubernetes Version (use kubectl version): 1.16
• OS (e.g. from /etc/os-release):

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  • fix(frontend): fixes empty page. Fixes #1234
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  • chore: set up changelog generation tools
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  • test: fix CI failure. Part of #1234
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[kubeflow-bot]

This change is 

[drewbutlerbb4]

/lgtm

[animeshsingh]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: animeshsingh

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