sslniff not working on ubuntu-bionic-18.04-amd64

Hi everyone,

Very interested to get this working, but have some errors ... any way I can proceed ?

```sudo python3 sslsniff.py
/virtual/main.c:27:17: warning: implicit declaration of function 'bpf_probe_read_user' is invalid in C99 [-Wimplicit-function-declaration]
bpf_probe_read_user(&__data.v0, sizeof(__data.v0), buf);
^
/virtual/main.c:63:17: warning: implicit declaration of function 'bpf_probe_read_user' is invalid in C99 [-Wimplicit-function-declaration]
bpf_probe_read_user(&__data.v0, sizeof(__data.v0), (char *)*bufp);
^
2 warnings generated.
LLVM ERROR: Program used external function 'bpf_probe_read_user' which could not be resolved!
```

```
sudo ./sslsniff
Traceback (most recent call last):
File "./sslsniff", line 156, in
pid=args.pid or -1)
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 1005, in attach_uprobe
(path, addr) = BPF._check_path_symbol(name, sym, addr, pid)
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 745, in _check_path_symbol
raise Exception("could not determine address of symbol %s" % symname)
Exception: could not determine address of symbol PR_Write
```