Update CI badges (#64)

Author: omus

README.md

@@ -1,7 +1,6 @@
 # FixedPointDecimals
 
-[![Travis Build Status](https://travis-ci.org/JuliaMath/FixedPointDecimals.jl.svg?branch=master)](https://travis-ci.org/JuliaMath/FixedPointDecimals.jl)
-[![Appveyor Build Status](https://ci.appveyor.com/api/projects/status/edir9h23fs98jfjc/branch/master?svg=true)](https://ci.appveyor.com/project/omus/fixedpointdecimals-jl)
+[![CI](https://github.com/JuliaMath/FixedPointDecimals.jl/workflows/CI/badge.svg)](https://github.com/JuliaMath/FixedPointDecimals.jl/actions?query=workflow%3ACI)
 [![coveralls](https://coveralls.io/repos/github/JuliaMath/FixedPointDecimals.jl/badge.svg?branch=master&service=github)](https://coveralls.io/github/JuliaMath/FixedPointDecimals.jl?branch=master)
 [![codecov.io](https://codecov.io/github/JuliaMath/FixedPointDecimals.jl/coverage.svg?branch=master)](https://codecov.io/github/JuliaMath/FixedPointDecimals.jl?branch=master)