nvim: Update theme to gruvbox

The default theme is hard to tell colors apart and the default color
schemes aren't great in general

Signed-off-by: Nicholas Mello <nick@nmello.dev>

nvim/lua/plugins/theme.lua

@@ -0,0 +1,10 @@
+return {
+  "ellisonleao/gruvbox.nvim",
+  config = function()
+    vim.g.gruvbox_contrast_dark = "hard"
+    vim.g.gruvbox_italic = 1
+    vim.g.gruvbox_bold = 1
+
+    vim.cmd("colorscheme gruvbox")
+  end,
+}