This commit provides a modified Go runtime in Docker image.
Now we can build a Go program using `occlum-go`, then run it
in SGX enclaves by Occlum.
The Golang demo demonstrates how to build and run a web server
program written in Go.
Fix std::alloc::Alloc not found
The lastest Rust changes the trait to std::alloc::AllocRef.
Update the docker files to support sgx 2.9.1
Remove the compilerRT dependency for rust sdk update
