Update main.py

As i was trying to run the script it raised the error.
Traceback (most recent call last):
  File "c:/Users/zedthecode/Desktop/zedlab/gui/tube.py", line 13, in <module>
    if a == "shutdown":
NameError: name 'a' is not defined

Author: deltabytesyt

Youtube Downloader With GUI/main.py

@@ -10,7 +10,7 @@
 file_size = 0
 
 q= input("")
-if a == "shutdown":
+if q == "shutdown":
     os.system("shutdown -s")
 #function progress to keep check of progress of function.
 def progress(stream=None, chunk=None,  remaining=None):