 error: libunwind.so: cannot open shared object file: No such file or directory

`python3.6 -m vmprof --mem --web myscript.py`
I tried on CentOS 6.5 and Ubuntu 16. Both of them gave me this error.

Full message:
```
could not load libunwind at runtime. error: libunwind.so: cannot open shared object file: No such file or directory
Uploading to http://vmprof.com...
 => Uploading the cpu profile...
      http://vmprof.com/#/xxx
```

