fix: replace vertsplit highlights wtih winseparator (#969)

From v0.7, vertsplit => WinSeparator so updated the nvimtreeversplit hl group too https://github.com/kyazdani42/nvim-tree.lua/pull/1219

lua/colors/highlights.lua

@@ -61,7 +61,7 @@ fg("StatusLineNC", one_bg3 .. " gui=underline")
 
 fg("LineNr", grey)
 fg("NvimInternalError", red)
-fg("VertSplit", one_bg2)
+fg("WinSeparator", one_bg2)
 
 if ui.transparency then
    bg("Normal", "NONE")
@@ -106,7 +106,7 @@ bg("NvimTreeNormalNC", darker_black)
 fg("NvimTreeOpenedFolderName", folder_bg)
 fg("NvimTreeRootFolder", red .. " gui=underline") -- enable underline for root folder in nvim tree
 fg_bg("NvimTreeStatuslineNc", darker_black, darker_black)
-fg_bg("NvimTreeVertSplit", darker_black, darker_black)
+fg_bg("NvimTreeWinSeparator", darker_black, darker_black)
 fg_bg("NvimTreeWindowPicker", red, black2)
 
 -- Telescope
@@ -130,7 +130,7 @@ if ui.transparency then
    bg("NvimTreeNormal", "NONE")
    bg("NvimTreeNormalNC", "NONE")
    bg("NvimTreeStatusLineNC", "NONE")
-   fg_bg("NvimTreeVertSplit", grey, "NONE")
+   fg_bg("NvimTreeWinSeparator", grey, "NONE")
 
    -- telescope
    bg("TelescopeBorder", "NONE")