Remove ruby-dev from travis config.
diff --git a/.travis.yml b/.travis.yml
index dbc372b..7393c41 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -74,7 +74,6 @@
       - python3-dev
       - liblua5.2-dev
       - lua5.2
-      - ruby-dev
       - cscope
 
 before_install: