Lexer: fix path token regex
Lexer: fix path token regex

Do not require the trailing colon for path in an attach point, since it
may not be present and then the parser fails with strange error.

Leading colon must always be present as path must follow the probe type
specifier (e.g. "uprobe:/bin/bash").

iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace