Update source copy with tar to pass `-f -` option

While trying to build OTP-17.0.2 on PC-BSD, I received this error:

cdykes@pcbsd:~$ erln8 --build --tag OTP-17.0.2 --id 17.0.2 CC=gcc46
Repo not specified, using default
defaultUsing default config
Building 17.0.2 from tag/branch OTP-17.0.2 of repo default
Custom build config:
Custom build env:
Build log: /usr/home/cdykes/.erln8.d/logs/build_17.0.2_2014-06-06T03:26:02.266760Z
[0] copy source                    tar: Error opening archive: Failed to
open '/dev/sa0'
[0] copy source
Here are the last 10 lines of the log file:
tail: /usr/home/cdykes/.erln8.d/logs/build_17.0.2_2014-06-06T03:26:02.266760Z: No such file or directory
ERROR: Cannot run tail -10 on /usr/home/cdykes/.erln8.d/logs/build_17.0.2_2014-06-06T03:26:02.266760Z

Using the `-f -` option instructs tar to use the STDIN and successfully eliminated the error.