Use rbx-2 in .travis.yml
Change debug log level to warn in in_syslog

Pattern mismatch log should be warn for early detection.
We can disable this message by `log_level error` in production.

In addition, change receive_data(_parser) rescue log level to error
because it catches unexpected error so not debug / warn level.
Use exception variable instead of ' st'
Remove unused method
Merge pull request #364 from fluent/change-debug-to-warn-in_syslog

Change debug log level to warn in in_syslog
Fix README typos
Merge pull request #366 from chibicode/patch-1

Fix README typos
fix out_file formatter
Fix typo of CONTRIBUTING
use config_param
Merge pull request #367 from sonots/fix_out_file_formatter

fix timezone issue of out_file formatter
fix to use rake argument to run specified test only
remove used env value from ENV, not to affect to any other code
revert 38fbd7a20f1ac40ef74675c4440c6bf40541de61 and bf573f272821cfcea0cc476028ec5b7172ddd141, then add comment for test execution