Update SUMMARY.md

Author: mzhang28

SUMMARY.md

@@ -8,7 +8,7 @@
    * [35 - A Simple Cipher](035-a-simple-cipher.md)
    * [35 - Python Basics 2 (TODO)](035-python-basics-2.md)
    * [35 - Linux Basics 2](035-linux-basics-2.md)
-   * [40 - QR (TODO)](040-qr.md)
+   * [40 - QR](040-qr.md)
    * [40 - Networking (TODO)](040-networking.md)
    * [40 - Lines, Dots, and Shift Keys (TODO)](040-lines-dots-shift-keys.md)
    * [40 - Linux Basics 3](040-linux-basics-3.md)