Error signing Jarfile with -b flag

When I try to sign a jarfile with -b (`keybase pgp sign -i myfile.jar -b -o myfile.jar.sig`) the operation fails, and the only information outputted to the terminal window is `- WARNING error closing Sink: stream wasn't found`

To reproduce, simply compile a Java jarfile, the contents don't seem to matter, and try to sign the file with -b flag.

my log id: f5f3e3c1507808c890c2fb1c

Reproduce the issue by compiling a Java JAR and running `keybase pgp sign -i myfile.jar -b -o myfile.jar.sig`; inspect the `stream wasn't found` warning and the log identified as `f5f3e3c1507808c890c2fb1c`. Done means the command signs the JAR successfully and produces the requested `.sig` file.

Written by the indexing model from the issue text.