Adding YangLexer.tokens to .gitignore.

Change-Id: I4b4fe725fa10d35f94af2080c608626da7af2bc2
diff --git a/.gitignore b/.gitignore
index c5aefb5..91638cd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,3 +13,4 @@
 .idea
 *.DS_Store
 /bin/
+YangLexer.tokens
\ No newline at end of file