Capture stderr from bower command.

[mhess]

[Fixes #83982738]

[flavorjones]

Open3 doesn't work in JRuby, pending fixing of this issue. As such, let's wait until a version of JRuby is released where this won't break it.

See related commit 86f47a6

Alternatively, you should feel free to resubmit this using "2>&1" shell redirection, as a temporary workaround.

[flavorjones]

I'd also love to see some cucumber features for bower support. There aren't any, and so this isn't an apparent failure when running the test suite.

[mhess]

I'm hesitant to redirect stderr to stdout because then there's extra parsing to do. Is redirecting stderr to "/dev/null" a platform-independent enough solution?