Update mappers.js

When I code NES games, I often use the following code in order to handle the controller:
```
        LDX #9
        STX $4016
        DEX
        STX $4016
    loop:
        LDA $4016
        DEX
        BNE loop
```
This works because when I write a 9 followed by an 8 to the controller, the only bit that actually counts is the LSB. The original code requires me to write exactly a 1, but that seems restrictive, and is not consistent with other emulators.