Cannot supply constant override if constant name returns digit

**This works:**

```
#define constant LMAO_TOKEN = 0xcccccccccccccccccccccccccccccccccccccccc
```

Command: `huffc -b src/MyThing.huff -c LMAO_TOKEN=0x1079873`

**This doesn't:**

```
#define constant ERC20_TOKEN = 0xcccccccccccccccccccccccccccccccccccccccc
```

Command: `huffc -b src/MyThing.huff -c ERC20_TOKEN=0x1079873`