Numbers should manifest with same string representation as other programming environments

```javascript
$ cat foo.jsonnet
0.9

$ jsonnet foo.jsonnet
0.90000000000000002
```

Not sure if there's a formal standard, but everyone else seems to agree on printing it one particular way, so maybe just follow that:

```bash
$ echo "print 0.9" | python
0.9
$ echo "console.log(0.9)" | node
0.9
$ echo "println(0.9)" | scala
0.9
```