Fix --stop-at-end for piped input

[jonscheiding]

The --stop-at-end flag doesn't work when piping input.

$(gource --log-command git) > repo.log

# Exits as expected
gource --stop-at-end repo.log

# Never exits
cat repo.log | gource --stop-at-end --log-format git - 

After building with this change, we can see:

$(gource --log-command git) > repo.log

# Exits as expected
gource --stop-at-end repo.log

# Exits as expected
cat repo.log | gource --stop-at-end --log-format git - 

We also see that tail -f repo.log | gource --stop-at-end --log-format git - exits, which IMO it should not. This is addressed by https://github.com/acaudwell/Core/pull/14.