filter-lamely: fix a typo

Signed-off-by: Elijah Newren <newren@gmail.com>

contrib/filter-repo-demos/filter-lamely

@@ -81,7 +81,7 @@ Intentional differences from git-filter-branch:
     differently depending on topology of commits instead of contents of files
     and is thus adversely affected by this change.  I doubt it, though.
   * I vastly simplified the map() function to just ignore writing out the
-    mapping; I've never seen anyone explicity use it, and filter-repo
+    mapping; I've never seen anyone explicitly use it, and filter-repo
     handles remapping to ancestors without it.  I dare you to find anyone
     that was reading the $workdir/../map/ directory and using it in their
     filtering.