added nexpr to list of test files in release_instructions
added nexpr to list of test files in release_instructions

nimble-dev/nimble,NLMichaud/nimble,nimble-dev/nimble,NLMichaud/nimble,nxdao2000/nimble,nimble-dev/nimble,nxdao2000/nimble,nxdao2000/nimble,nxdao2000/nimble,nimble-dev/nimble,nimble-dev/nimble,NLMichaud/nimble,NLMichaud/nimble