Fix typos

CHANGES.md

@@ -9,10 +9,10 @@
       topydo -t done.txt completed:today # if auto-archiving is set
 
 * `ls -F` supports `%P` that expands to a single space when no priority is set,
-  in contrast to `%p' which expands to an empty string (thanks to @MinchinWeb).
+  in contrast to `%p` which expands to an empty string (thanks to @MinchinWeb).
 * `ls -N` prints enough todo items such that it fits on one screen (thanks to
   @MinchinWeb).
-* Aliases can have a `{}` placeholder which is substitude with the alias'
+* Aliases can have a `{}` placeholder which is substituted with the alias'
   arguments.
 * `pri` accepts priorities in lowercase (thanks to @MinchinWeb).
 * Several bugfixes for `dep gc`.