Numeric calculations in go-jsonnet and cpp-jsonnet produce (slightly) different numbers

I've found some cases where go-jsonnet doesn't match jsonnet.

C++ jsonnet:
```
$ ./jsonnet -e "36.557601928710938 + std.cos(2 * 3.14159265358979323846264338327950288 / 32 * 15) * 2"
34.596031367904473
$ ./jsonnet -e "38.19 + std.cos(2 * 3.14159265358979323846264338327950288 / 32 * 15) * 2"
36.228429439193533
```

go-jsonnet:
```
$ ./jsonnet -e "36.557601928710938 + std.cos(2 * 3.14159265358979323846264338327950288 / 32 * 15) * 2"
34.59603136790448
$ ./jsonnet -e "38.19 + std.cos(2 * 3.14159265358979323846264338327950288 / 32 * 15) * 2"
36.22842943919354
```