docs: remove broken badge links (#1672)

README.md

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 # Tedious (node implementation of TDS)
-[![Dependency Status](https://david-dm.org/tediousjs/tedious.svg)](https://david-dm.org/tediousjs/tedious) [![NPM version](https://badge.fury.io/js/tedious.svg)](http://badge.fury.io/js/tedious) [![Build Status](https://secure.travis-ci.org/tediousjs/tedious.svg)](http://travis-ci.org/tediousjs/tedious) [![Build Status](https://ci.appveyor.com/api/projects/status/ike3p58hljpyffrl?svg=true)](https://ci.appveyor.com/project/tediousjs/tedious) [![Slack Status](https://tediousjs-slack.herokuapp.com/badge.svg)](https://tediousjs-slack.herokuapp.com/)[![Code Coverage](https://codecov.io/gh/tediousjs/tedious/badge.svg)](https://codecov.io/gh/tediousjs/tedious)
+[![NPM version](https://badge.fury.io/js/tedious.svg)](http://badge.fury.io/js/tedious) [![Build Status](https://ci.appveyor.com/api/projects/status/ike3p58hljpyffrl?svg=true)](https://ci.appveyor.com/project/tediousjs/tedious) [![Code Coverage](https://codecov.io/gh/tediousjs/tedious/badge.svg)](https://codecov.io/gh/tediousjs/tedious)
 
 
 Tedious is a pure-Javascript implementation of the [TDS protocol](http://msdn.microsoft.com/en-us/library/dd304523.aspx),