Ignore composer vendor directory

Signed-off-by: Alex Bilbie <alex@alexbilbie.com>
diff --git a/.gitignore b/.gitignore
index 11fb6d6..a035c2b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,4 +11,5 @@
 user_guide_src/build/*
 user_guide_src/cilexer/build/*
 user_guide_src/cilexer/dist/*
-user_guide_src/cilexer/pycilexer.egg-info/*
\ No newline at end of file
+user_guide_src/cilexer/pycilexer.egg-info/*
+/vendor/
\ No newline at end of file