Fix binding with shift to go- command not passing shift

Our codebase contained something like:

    CodeMirror.keyMap.basic["Up"] = moveUpAcrossRegions;

Where `moveUpAcrossRegions` used `moveV` internally. Shift-selections
weren't working. Documentation stated that shift is passed through for
"go" prefixed commands, so assumed this would work:

    CodeMirror.keyMap.basic["Shift-Up"] = "goLineDown";
    CodeMirror.keyMap.basic["Up"] = moveUpAcrossRegions;

But the shift was still being dropped. This commit makes the key event
handling properly passes it through.