Fixes isUUIDv3 and isUUIDv4

isUUIDv3() and isUUIDv4() were untested and there were a few issues I found while working with it. Made several changes:
1) adds missing return in each method
2) adds tests for each method
3) in isUUID(), changes str.match(pattern) to pattern.test(str) because the former returns the actual matches, while the later returns true/false

#3 Example:
```javascript
var x = 'some uuid v4';
validators.isUUIDv4(x)  // expected to return return true/false, but
                        // returned Array of matches
```
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match#Notes