remove GNU-specific usage for `sed` in shell example
remove GNU-specific usage for `sed` in shell example

This ensures that the shell example works with GNU and non-GNU `sed`.

bloomberg/blpapi-http,flojdek/blpapi-http,flojdek/blpapi-http,flojdek/blpapi-http,fyquah95/blpapi-http,flojdek/blpapi-http,fyquah95/blpapi-http,fyquah95/blpapi-http,bloomberg/blpapi-http,bloomberg/blpapi-http,flojdek/blpapi-http