Added .sh ending to bootstrapd's init script

Apparently [some Travis boxes](https://s3.amazonaws.com/archive.travis-ci.org/jobs/32898006/log.txt) executed 
```sh
gcc -Ofast -Wall -Wextra    ../other/bootstrap_daemon/tox-bootstrapd.c   -o ../other/bootstrap_daemon/tox-bootstrapd
```
during `make dist` stage, which caused issues since "../other/bootstrap_daemon/tox-bootstrapd" is an init script.