fix: make compatible with symlinked repository

Resolves #9

Author: Matthias Günter

src/Comcast/PhpLegalLicenses/Command/GenerateCommand.php

@@ -91,7 +91,7 @@ protected function getTextForDependency($dependency)
         $description = isset($dependency['description']) ? $dependency['description'] : 'Not configured.';
         $version = $dependency['version'];
         $homepage = isset($dependency['homepage']) ? $dependency['homepage'] : 'Not configured.';
-        $sha = str_split($dependency['source']['reference'], 7)[0];
+        $sha = isset($dependency['source']) ? str_split($dependency['source']['reference'], 7)[0] : 'no sha';
         $licenseNames = isset($dependency['license']) ? implode(', ', $dependency['license']) : 'Not configured.';
         $license = $this->getFullLicenseText($name);