Add tex completion for deoplete

vim/ftplugin/tex.vim

@@ -1,8 +1,15 @@
 let g:vimtex_imaps_leader='?'
 if !has("nvim")
     let g:vimtex_compiler_latexmk ={
-    \   'backend' : 'jobs'
-    \}
+                \   'backend' : 'jobs'
+                \}
+endif
+
+if has("nvim")
+    if !exists('g:deoplete#omni#input_patterns')
+        let g:deoplete#omni#input_patterns = {}
+    endif
+    let g:deoplete#omni#input_patterns.tex = g:vimtex#re#deoplete
 endif
 
 set conceallevel=0