Change terminal ESC to <C-j><C-j>

It was difficult being inside another vim instance where jj is also the
escape.

.vimrc

@@ -97,7 +97,7 @@ nnoremap <C-]> :tabnext<cr>
 if has('nvim')
   let g:airline#themes#dark#palette.terminal = copy(g:airline#themes#dark#palette.insert)
 
-  tnoremap jj <C-\><C-N>
+  tnoremap <C-j><C-j> <C-\><C-N>
   tmap <C-[> <C-\><C-N><C-[>
   tmap <C-]> <C-\><C-N><C-]>
   tmap <C-W> <C-\><C-N><C-W>