SelfUpdateCommand should not expect package version to be ready for normalization

[Chi-teck]

Some projects use version as a placeholder that is dynamically updated when PHAR file is built.

Example:
gordalina/cachetool#231

I think the current implementation should be updated to something like follows.

try {
  $this->currentVersion = $version_parser->normalize($currentVersion);
}
catch (UnexpectedValueException) {
  $this->currentVersion = 'Unknown';
}