utils/get-developers: fix python 3.x compatibility

utils/get-developers: fix python 3.x compatibility

This fixes a syntax error introduced in bcf2ed5cc3.

Output before the patch:
    $ ./utils/get-developers outgoing/*
        File "./utils/get-developers", line 97
            print dev
                    ^
        SyntaxError: Missing parentheses in call to 'print'. Did you mean
        print(dev)?

Output after the patch:
    $ ./utils/get-developers outgoing/*
    git send-email --to buildroot@buildroot.org

Signed-off-by: Grégoire Delattre <gregoire.delattre@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>