I want to get full number as a `String`, but instead `"1490650000000"` it returns scientific notation `"1.49065e+12"`

Here's how I try to convert it:

```
{$substr: ["$myNumber", 0, -1]};

```

Any ideas how to prevent it? 

**Note:**
I'm using v3.6 and can't upgrade to use `$toString` (thanks mlab).