Fix travis build badge link
Fix travis build badge link

[] fixed the link to the image, but the hyperlink to the travis site itself was left out. This CL fixed that.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=228241047

google/nomulus,google/nomulus,google/nomulus,google/nomulus,google/nomulus,google/nomulus