Remove travis-ci badge

[aledbf]

What this PR does / why we need it:

Because we switched to prow. There is no badge but we can see the status in tesgrid https://testgrid.k8s.io/sig-network-ingress-nginx#Summary

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [aledbf]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@5dfc7e2). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #4223   +/-   ##
=========================================
  Coverage          ?   57.95%           
=========================================
  Files             ?       87           
  Lines             ?     6536           
  Branches          ?        0           
=========================================
  Hits              ?     3788           
  Misses            ?     2320           
  Partials          ?      428

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