Convert cache to es6 class
Convert cache to es6 class

Signed-off-by: Sina Mahmoodi <5efde75dc89cf3dd6979127c39f2579ba2efcec2@gmail.com>

ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-vm,ethereum/ethereumjs-vm,ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-vm