vendor.py: fix typo in licenses_used.txt comment

BUG=None
TEST=python vendor.py

Change-Id: Ia271979e5431a67b519142987a7cfcba162f5501
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/rust_crates/+/3879291
Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Auto-Submit: Daniel Verkamp <dverkamp@chromium.org>
Tested-by: Daniel Verkamp <dverkamp@chromium.org>
diff --git a/vendor.py b/vendor.py
index 1b7bf2a..bb05e72 100755
--- a/vendor.py
+++ b/vendor.py
@@ -558,7 +558,7 @@
         header = textwrap.dedent(
             """\
             # File to describe the licenses used by this registry.
-            # Used to it's easy to automatically verify ebuilds are updated.
+            # Used so it's easy to automatically verify ebuilds are updated.
             # Each line is a license. Lines starting with # are comments.
             """
         )