Fixed documentation

Author: kmvanbrunt

CHANGELOG.md

@@ -10,7 +10,7 @@
     * Aliases are now sorted alphabetically
     * The **set** command now tab-completes settable parameter names
     * Added ``async_alert``, ``async_update_prompt``, and ``set_window_title`` functions
-        * These allow you to provide feedback to the user in an asychronous fashion, meaning alert can be
+        * These allow you to provide feedback to the user in an asychronous fashion, meaning alerts can
         display when the user is still entering text at the prompt. See [async_printing.py](https://github.com/python-cmd2/cmd2/blob/master/examples/async_printing.py)
         for an example.
 * Deletions