change "local" declaration to "var"

disable local function, all function will be
locally by default.

declare local scope variable:
	var i = 1

Bytecode generate:
	./ktap -b -e 'var i = 1'
	sizecode: 2
	00000001        LOADK           i <- 1
	00800023        RETURN

declare global scope variable:
	i = 1

Bytecode generate:
	./ktap -b -e 'i = 1'
	sizecode: 2
	80404008        SETTABUP        global{i} <- 1
	00800023        RETURN

TODO: variable must be declared with "var".

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>