.travis.yml: rbconfig.rb is not needed to setup sources

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66603 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

.travis.yml

@@ -328,6 +328,7 @@ before_script:
     mkdir ~/.downloaded-cache
   - ln -s ~/.downloaded-cache
   - "> config.status"
+  - "> .rbconfig.time"
   - sed -f tool/prereq.status Makefile.in common.mk > Makefile
   - make -s $JOBS update-download
   - make -s $JOBS srcs