Failing test with current Integer Generator

```
1) Eris\Generator\IntegerTest::testShouldEventuallyGenerateAllTheValues
Only generated the following values: array (
        0 => 5,
        1 => 4,
        2 => 3,
        3 => 6,
        )
Failed asserting that 4 matches expected 5.
```
Because when we reach the limit of the Integers the behaviour is different :-)
```php
php > for ($i = 0; $i < 20; $i++) { var_dump(rand(PHP_INT_MIN -1, PHP_INT_MAX)); }
int(-261974150149570560)
int(-8336983343505604608)
int(0)
int(-2994400921884033024)
int(-3233165867629936640)
int(-3853316444607479808)
int(0)
int(-998058229592227840)
int(-7712278864243720192)
int(-1234161712953819136)
int(0)
int(0)
int(-2863952577442086912)
int(-9176052389289918464)
int(-8661246021369593856)
int(-7190840594371969024)
int(-3118635264692453376)
int(-4602218175340216320)
int(-1479849570455257088)
int(-1363854856116240384)
```

And strange... Look if I go away from the lower limit by 100:
```php
php > for ($i = 0; $i < 20; $i++) { var_dump(rand(PHP_INT_MIN + 100, PHP_INT_MAX)); }
int(-5534939970856288156)
int(-148888219591638940)
int(100)
int(-3896174737843290012)
int(100)
int(-643664243022888860)
int(100)
int(100)
int(100)
int(100)
int(-2883224946102763420)
int(-4092853874581307292)
int(100)
int(-2223207572150681500)
int(-4686796097262190492)
int(-1306333965438680988)
int(-1001064174123483036)
int(-3248206877460266908)
int(-5624645276275834780)
int(100)
```