choosenim does not work on Linux with musl
As in the title, trying to run `curl https://nim-lang.org/choosenim/init.sh -sSf | sh` on a musl based Linux distro results in:

```
choosenim-init: Downloading choosenim-0.6.0_linux_amd64
sh: /tmp/choosenim-0.6.0_linux_amd64: not found
```

This is because choosenim is linked against glibc:

```
thermi:~$ ldd /tmp/choosenim-0.6.0_linux_amd64 
        /lib64/ld-linux-x86-64.so.2 (0x7fc250e12000)
        librt.so.1 => /lib64/ld-linux-x86-64.so.2 (0x7fc250e12000)
        libdl.so.2 => /lib64/ld-linux-x86-64.so.2 (0x7fc250e12000)
        libc.so.6 => /lib64/ld-linux-x86-64.so.2 (0x7fc250e12000)
Error relocating /tmp/choosenim-0.6.0_linux_amd64: __fdelt_chk: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: __poll_chk: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: __strdup: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: __memcpy_chk: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: gnu_dev_major: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: __longjmp_chk: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: gnu_dev_minor: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: __fprintf_chk: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: gnu_dev_makedev: symbol not found
Error relocating /tmp/choosenim-0.6.0_linux_amd64: __sprintf_chk: symbol not found
```