Remove Appveyor script (#145)

* Remove appveyor script

* Update badges in Readme

Author: jishnub

README.md

@@ -3,8 +3,7 @@ Support for orthogonal polynomial-based spaces in ApproxFun
 
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 [![](https://img.shields.io/badge/docs-latest-blue.svg)](https://JuliaApproximation.github.io/ApproxFun.jl/latest)
-[![Build Status](https://travis-ci.org/JuliaApproximation/ApproxFunOrthogonalPolynomials.jl.svg?branch=master)](https://travis-ci.org/JuliaApproximation/ApproxFunOrthogonalPolynomials.jl) 
-[![Build status](https://ci.appveyor.com/api/projects/status/5v72sch3ci5l77e3?svg=true)](https://ci.appveyor.com/project/dlfivefifty/approxfunorthogonalpolynomials-jl)
+[![CI](https://github.com/JuliaApproximation/ApproxFunOrthogonalPolynomials.jl/actions/workflows/ci.yml/badge.svg)](https://github.com/JuliaApproximation/ApproxFunOrthogonalPolynomials.jl/actions/workflows/ci.yml)
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 [![deps](https://juliahub.com/docs/ApproxFunOrthogonalPolynomials/deps.svg)](https://juliahub.com/ui/Packages/ApproxFunOrthogonalPolynomials/bk9eW?t=2)
 [![version](https://juliahub.com/docs/ApproxFunOrthogonalPolynomials/version.svg)](https://juliahub.com/ui/Packages/ApproxFunOrthogonalPolynomials/bk9eW)