Fix close tag on keyboard shortcut page (#179)

Author: mgeisler

src/running-the-course/keyboard-shortcuts.md

@@ -2,7 +2,7 @@
 
 There are several useful keyboard shortcuts in mdBook:
 
-* <kbd>Arrow-Left</kdb>: Navigate to the previous page.
+* <kbd>Arrow-Left</kbd>: Navigate to the previous page.
 * <kbd>Arrow-Right</kbd>: Navigate to the next page.
 * <kbd>Ctrl + Enter</kbd>: Execute the code sample that has focus.
 * <kbd>s</kbd>: Activate the search bar.