Remove travis ci status in README.md (#371)

Author: mohanson

README.md

@@ -1,6 +1,5 @@
 # [Nervos CKB](https://nervos.org) VM
 
-[![Build Status](https://travis-ci.com/nervosnetwork/ckb-vm.svg?branch=master)](https://travis-ci.com/nervosnetwork/ckb-vm)
 [![Build Status](https://dev.azure.com/nervosnetwork/ckb-vm/_apis/build/status/nervosnetwork.ckb-vm?branchName=develop)](https://dev.azure.com/nervosnetwork/ckb-vm/_build/latest?definitionId=10&branchName=develop)
 [![codecov](https://codecov.io/gh/nervosnetwork/ckb-vm/branch/develop/graph/badge.svg)](https://codecov.io/gh/nervosnetwork/ckb-vm)