Reports/GitBlame: Fix invocation path of git blame

After we change into the files directory, invocation of git blame with full path will end in fatal error.

src/Reports/Gitblame.php

@@ -70,7 +70,7 @@ protected function getBlameContent($filename)
         $cwd = getcwd();
 
         chdir(dirname($filename));
-        $command = 'git blame --date=short "'.$filename.'" 2>&1';
+        $command = 'git blame --date=short "'.basename($filename).'" 2>&1';
         $handle  = popen($command, 'r');
         if ($handle === false) {
             $error = 'ERROR: Could not execute "'.$command.'"'.PHP_EOL.PHP_EOL;