Gantt month misaligned in Month View

[KebabRonin]

Describe the bug
Month names are misalligned in the Month view mode in the taskgantt macro.

Steps to reproduce
Steps to reproduce the problematic behavior:

1. Create a task
2. In the taskgantt display, choose Month view mode

Expected behavior
Month names reflect the task dates.

Actual behavior
Month names are offset by 1.

Screenshots
Week view:

Month view:

Expected Month view:

Environment (please complete the following information):

• OS: linux
• Browser firefox
• XWiki version 14.10
• App version 3.7.0 (bug since 3.6.0)