Release 0.5.15

[hieudion]

Release 0.5.15
specify version 1.2.5 to tzinfo to avoid changes in 1.2.6 causes fail in UT.
More information:
https://travis-ci.org/treasure-data/embulk-input-mixpanel/jobs/638469421

/home/travis/build/treasure-data/embulk-input-mixpanel/test/test_range_generator.rb:40:in `test_1_fetch_day'
/home/travis/build/treasure-data/embulk-input-mixpanel/lib/range_generator.rb:14:in `generate_range'
/home/travis/build/treasure-data/embulk-input-mixpanel/lib/range_generator.rb:38:in `show_warnings'
/home/travis/build/treasure-data/embulk-input-mixpanel/lib/range_generator.rb:72:in `from_date_too_early?'
/home/travis/build/treasure-data/embulk-input-mixpanel/lib/range_generator.rb:76:in `today'
/home/travis/.rvm/gems/jruby-9.0.5.0/gems/activesupport-5.2.4.1/lib/active_support/values/time_zone.rb:234:in `[]'
/home/travis/.rvm/gems/jruby-9.0.5.0/gems/activesupport-5.2.4.1/lib/active_support/values/time_zone.rb:300:in `initialize'
/home/travis/.rvm/gems/jruby-9.0.5.0/gems/activesupport-5.2.4.1/lib/active_support/values/time_zone.rb:206:in `find_tzinfo'
/home/travis/.rvm/gems/jruby-9.0.5.0/gems/tzinfo-1.2.6/lib/tzinfo/timezone.rb:113:in `new'
/home/travis/.rvm/gems/jruby-9.0.5.0/gems/tzinfo-1.2.6/lib/tzinfo/timezone.rb:92:in `get'
/home/travis/.rvm/gems/jruby-9.0.5.0/gems/tzinfo-1.2.6/lib/tzinfo/zoneinfo_data_source.rb:211:in `load_timezone_info'
/home/travis/.rvm/gems/jruby-9.0.5.0/gems/tzinfo-1.2.6/lib/tzinfo/zoneinfo_timezone_info.rb:29:in `initialize'
Error: test_1_fetch_day(RangeGeneratorTest::GenerateRangeTest): ArgumentError: wrong number of arguments (0 for 1)

The syntax failure could be the jruby issue, issue itself I filed in tzinfo: tzinfo/tzinfo#114

[trung-huynh]

LGTM