fix(dev): showcase:generate outdir

[bshaffer]

use $targetDir rather than $outDir for showcase sync, to use the resolved path and to to be consistent with the "remove" line above it:

google-cloud-php/dev/src/Command/ShowcaseGenerateCommand.php

Line 181 in 7912a78

$this->fs->remove([$targetDir . '/src/V1beta1', $targetDir . '/metadata']);