Convert numeric inputs to string

I'm getting "TypeError: Expected a String" error when I pass a numeric values to Hyperglue, converting `str` to number will fix that

error stack was;

```
   at Object.exports.encode (/Users/azer/dev/brick-node/node_modules/hyperglue/node_modules/ent/index.js:13:15)
    at Result.setAttribute (/Users/azer/dev/brick-node/node_modules/hyperglue/node_modules/trumpet/index.js:285:51)
    at /Users/azer/dev/brick-node/node_modules/hyperglue/index.js:57:27
```