Remove note about using a fixed disk.

`vagrant package` command doesn't export the fixed disk.

Relates to 52fb1ab5caed401f6c50a82ae04ad291d746a37b
Use "." instead of "source" for POSIX compliance

"source" doesn't seem to be POSIX compatible. E.g. fails on Ubuntu where
/bin/sh is mapped to dash)
Remove -j option from date command
Merge branch 'shell-compatibility'

GH-11
Merge remote-tracking branch 'upstream/master'