Nord Pure style NvimTree

[Hierosme]

After many tests and read Nord Palette documentation, i propose a better version of the NvimTree

• Root Folder use nord15
• Directory and IndentMarker use nord4 color
• Folder name use nord 4 and file use nord4 color
• Opened folder use nord5 color
• Opened file use nord6 color

The result is smooth and look more natural.