Can't use "pipe" in Validators pattern

Version: v3.0.1

### Bug Description
Can not use "pipe" ("|") character in Validators pattern

### Steps To Reproduce
```
Validators::is('a', 'pattern:(a|b)');
// E_WARNING: preg_match(): Compilation failed: missing closing parenthesis at offset 1
```

### Expected Behavior
```
Validators::is('a', 'pattern:(a|b)');
// should return true
```
