Added Travis CI badge

README.md

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 #VisiOmatic
+[![Build Status](https://travis-ci.org/astromatic/visiomatic.svg?branch=master)](https://travis-ci.org/astromatic/visiomatic)
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 an [IIPImage] web client for visualizing science-grade, multi-channel astronomy images. VisiOmatic works essentially as a large [Leaflet] plug-in, providing subproperties to the original Leaflet "classes" with new or overloaded methods. It relies on the [iipsrv-astro] image server for pixel data and [Vizier] for catalog overlays. See on-line [documentation] and [demo]
 
 Only interested in an [IIPImage] plugin for [Leaflet]? Try [Leaflet.TileLayer.IIP](https://github.com/astromatic/Leaflet.TileLayer.IIP)