Fixed seo.robots template variable

It seems as if the seo.robots template variable is not being populated correctly. I was getting "undefined" even though it was defined in the seo options block. 

I added a simple block to fix this logic that checks if the template variables have a seo.robots block and if not then it falls back to the default / overridable options block.

```
// Make private pages noindex, nofollow
if (!data.seo.robots && data.private) {
  data.seo.robots = 'noindex, nofollow';
} else if ((data.seo.robots || options.seo.robots) && !data.private){
  //Get from file definition and fall back to options/defaults
  data.seo.robots = data.seo.robots ? data.seo.robots : options.seo.robots;
}
```

Let me know if I missed something. 
Can't you change this logic to be ```else if (!data.seo.robots && options.seo.robots)``` and then eliminate the ternary statement in the body?

You could add `&& !data.private` to be explicit, but that should be the case if we include `!data.seo.robots`.