Fix for setting of cookieSecure in tracker

Looking at the cookies I noticed that they are not set to be secure when the page is served over SSL.

Looking in tracker.js I spotted this:
```
    cookieSecure = SnowPlow.documentAlias.location.protocol === 'https',
```

This should read 
```
    cookieSecure = SnowPlow.documentAlias.location.protocol === 'https:',
```

I couldn't find any tests so I'm having a look at writing some with Jasmine (I'll do this separately from this change.)