4c11e56 script: remove bashisms

Authored and Committed by zuh0 3 years ago
    script: remove bashisms
    
    The shell check utility detected a bunch of problems regarding POSIX
    compliance for the `arm-image-installer` script. This commit fixes them
    all and removes all `shellcheck`'s warnings.
    
    Signed-off-by: Gabriel Duque <gabriel@zuh0.com>
    
        
file modified
+33 -31