fix: cmp-omni messes with the lsp completion

If we use cmp-omni and lsp together, it seems that it will mess the
autocompletion. So we only use it with tex file, where lsp in not used.

README.md

@@ -13,7 +13,7 @@
       <img alt="Latest release" src="https://img.shields.io/github/v/release/jdhao/nvim-config" />
     </a>
     <a href="https://github.com/neovim/neovim/releases/tag/stable">
-      <img src="https://img.shields.io/badge/Neovim-0.8.0-blueviolet.svg?style=flat-square&logo=Neovim&logoColor=green" alt="Neovim minimum version"/>
+      <img src="https://img.shields.io/badge/Neovim-0.8.1-blueviolet.svg?style=flat-square&logo=Neovim&logoColor=green" alt="Neovim minimum version"/>
     </a>
     <a href="https://github.com/jdhao/nvim-config/search?l=vim-script">
       <img src="https://img.shields.io/github/languages/top/jdhao/nvim-config" alt="Top languages"/>
@@ -21,8 +21,8 @@
     <a href="https://github.com/jdhao/nvim-config/graphs/commit-activity">
       <img src="https://img.shields.io/github/commit-activity/m/jdhao/nvim-config?style=flat-square" />
     </a>
-    <a href="https://github.com/jdhao/nvim-config/releases/tag/v0.8.0">
-      <img src="https://img.shields.io/github/commits-since/jdhao/nvim-config/v0.8.0?style=flat-square" />
+    <a href="https://github.com/jdhao/nvim-config/releases/tag/v0.8.1">
+      <img src="https://img.shields.io/github/commits-since/jdhao/nvim-config/v0.8.1?style=flat-square" />
     </a>
     <a href="https://github.com/jdhao/nvim-config/graphs/contributors">
       <img src="https://img.shields.io/github/contributors/jdhao/nvim-config?style=flat-square" />

init.lua

@@ -12,7 +12,7 @@ local api = vim.api
 local utils = require("utils")
 
 -- check if we have the latest stable version of nvim
-local expected_ver = "0.8.0"
+local expected_ver = "0.8.1"
 local nvim_ver = utils.get_nvim_version()
 
 if nvim_ver ~= expected_ver then

lua/config/nvim-cmp.lua

@@ -35,7 +35,6 @@ cmp.setup {
     { name = "ultisnips" }, -- For ultisnips user.
     { name = "path" }, -- for path completion
     { name = "buffer", keyword_length = 2 }, -- for buffer word completion
-    { name = "omni" },
     { name = "emoji", insert = true }, -- emoji completion
   },
   completion = {
@@ -61,6 +60,15 @@ cmp.setup {
   },
 }
 
+cmp.setup.filetype("tex", {
+  sources = {
+    { name = "omni" },
+    { name = "ultisnips" }, -- For ultisnips user.
+    { name = "buffer", keyword_length = 2 }, -- for buffer word completion
+    { name = "path" }, -- for path completion
+  },
+})
+
 --  see https://github.com/hrsh7th/nvim-cmp/wiki/Menu-Appearance#how-to-add-visual-studio-code-dark-theme-colors-to-the-menu
 vim.cmd([[
   highlight! link CmpItemMenu Comment