Lowercase abbreviations throws error

[stefanzweifel]

1. What's your issue?

The package throws an exception, if the provided abbreviation is not in uppercase.

2. Which PHP Version are you using?

I'm using PHP Version 7.0.

3. Which Version of the php-swiss-cantons Package are you using?

I'm using version 1.2.0.

5. What did you expect to happen in the first place?

The following code snippet shouldn't throw an exception.

$canton = $cantonManager->getByAppreviation('zh');