Update nginx.tmpl

[damiendurant]

Disable server_tokens (remove nginx version from error pages and headers)

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[k8s-reviewable]

This change is 

[damiendurant]

I signed it!

[aledbf]

@damiendurant the development of ingress is now located in https://github.com/kubernetes/ingress.
This feature is already proposed kubernetes/ingress-nginx#94

[aledbf]

@damiendurant please close this PR

[damiendurant]

Thanks.
I close so.