Make stdout and stderr utf8

It seems stdout and stderr are not in utf8, so commands such as rbm/rbm showconf browser build --target torbrowser-windows-x86_64 --target nightly --target testbuild in tor-browser-build will not show correctly the character Â© (used in projects/browser/windows-installer.nsi) correctly when the terminal is in utf8.

/cc @pierov

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