Fix (- 1) and (incf/decf x 5)
Fix (- 1) and (incf/decf x 5)

Fix the following incorrect (or at least unexpected) behavior in
ParenScript.

(js (- 1))  =>  "1;"
(js (incf x 5))   => an error
(js (decf x 5))   => an error

Signed-off-by: Attila Lendvai <9bfb612348e3e33379fbef6141469f64be0a104c@gmail.com>

JDReutt/parenscript,vsedach/Parenscript,fredericksilva/Parenscript,manuel/parenscript,JackDanger/parenscript,3b/parenscript,VincentToups/parenscript,JackDanger/parenscript,JackDanger/parenscript