.travis.yml: do not ignore diff

* .travis.yml (before_script): confured results with/without cache
  must be same.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49802 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

.travis.yml

@@ -57,7 +57,7 @@ before_script:
   - "cp -pr config.status .ext/include config_1st"
   - "make reconfig"
   - "cp -pr config.status .ext/include config_2nd"
-  - "diff -ru config_1st config_2nd || true"
+  - "diff -ru config_1st config_2nd"
   - "make -s $JOBS encs"
   - "make -s $JOBS exts"
   - "make update-rubyspec"