fix: Check and convert types to string if not already

[tech2serve]

Some sites have trouble displaying meetings when the 11th Step Meditation
type, being sanitized to create css classes, throws an error because the
11 is an integer instead of a string.

It remains unclear why this only affects a small set of sites.

closes #257

[crispyatl]

There are a few issues here:

#1 Instead of:

typeClass = typeof obj.types[i] === 'string' ? obj.types[i] : obj.types[i].toString();
classes.push('type-' + sanitizeTitle(typeClass));

You can simply do:
classes.push('type-' + sanitizeTitle(obj.types[i].toString()));

#2 Instead of fixing this one field, we could fix future issues with any fields by doing the string conversion in sanitizeTitle(). Since the function deals with titles, whatever it is passed should be converted to a string if it isn't already. I will create a new PR for this.