remove travis build status badge

Author: isaacs

README.md

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 # node-tar
 
-[![Build Status](https://travis-ci.org/npm/node-tar.svg?branch=master)](https://travis-ci.org/npm/node-tar)
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 [Fast](./benchmarks) and full-featured Tar for Node.js
 
 The API is designed to mimic the behavior of `tar(1)` on unix systems.