The date format is wrong when the Calendar type is in Japanese date format(和暦)

Summary

The date format is wrong when the Calendar type is in Japanese date format(和暦)

Steps to Reproduce

1. Change the date setting of your computer to 和暦
   1. Select control panel
   2. Choose "Change date, time, or number formats"
   3. Select "Additional setings..."
   4. In the Date tab, select 和暦 from the Calendar type
2. Open Sourcetree and view the previous commits in the branch

Expected Results

The commit date will be 2018/MM/DD(or DD MM 2018)

Actual Results

The commit date is 4006/MM/DD(or DD MM 4006)

Workaround

Change Calendar type to English format(西暦)