CVE-2020-26213

In teler before version 0.0.1, if you run teler inside a Docker container and encounter `errors.Exit` function, it will cause denial-of-service (`SIGSEGV`) because it doesn't get process ID and process group ID of teler properly to kills. The issue is patched in teler 0.0.1 and 0.0.1-dev5.1.