Fix minor formatting issue.

docs/custom_quantum_functions.md

@@ -36,7 +36,7 @@ enum my_keycodes {
 
 ## Programming The Behavior Of Any Keycode
 
-When you want to override the behavior of an existing key, or define the behavior for a new key, you should use the `process_record_kb()' and `process_record_user()` functions. These are called by QMK during key processing before the actual key event is handled. If these functions return `true` QMK will process the keycodes as usual. That can be handy for extending the functionality of a key rather than replacing it. If these functions return `false` QMK will skip the normal key handling, and it will be up you to send any key up or down events that are required.
+When you want to override the behavior of an existing key, or define the behavior for a new key, you should use the `process_record_kb()` and `process_record_user()` functions. These are called by QMK during key processing before the actual key event is handled. If these functions return `true` QMK will process the keycodes as usual. That can be handy for extending the functionality of a key rather than replacing it. If these functions return `false` QMK will skip the normal key handling, and it will be up you to send any key up or down events that are required.
 
 These function are called every time a key is pressed or released.