Add missing .

Author: ZerozAndOnes

lib/pdf.js

@@ -153,7 +153,7 @@ PDF.prototype.exec = function PdfExec (callback) {
   // An exit event is most likely an error because we didn't get any data at this point
   child.on('close', respond)
   // According to child process documentation (https://nodejs.org/docs/latest-v14.x/api/child_process.html#child_process_event_exit), 
-  // exit event can fire before stdio is closed. Thus, it's probably not a good idea to subscribe to exit event at all
+  // exit event can fire before stdio is closed. Thus, it's probably not a good idea to subscribe to exit event at all.
   // on('close') above should be sufficient
   // child.on('exit', respond)