Revert "Make sure update/install after PlugUpgrade work"

This reverts commit 19b12e221694650723102dcb5d5704936a598b83.

No luck. The user still have to reload .vimrc anyway. Let's just make it
clear that a restart can be required after PlugUpgrade.

README.md

@@ -60,14 +60,14 @@ Reload .vimrc and `:PlugInstall` to install plugins.
 
 ### Commands
 
-| Command                           | Description                                                        |
-| --------------------------------- | ------------------------------------------------------------------ |
-| PlugInstall [name ...] [#threads] | Install plugins                                                    |
-| PlugUpdate [name ...] [#threads]  | Install or update plugins                                          |
-| PlugClean[!]                      | Remove unused directories (bang version will clean without prompt) |
-| PlugUpgrade                       | Upgrade vim-plug itself                                            |
-| PlugStatus                        | Check the status of plugins                                        |
-| PlugDiff                          | See the updated changes from the previous PlugUpdate               |
+| Command                           | Description                                                         |
+| --------------------------------- | ------------------------------------------------------------------- |
+| PlugInstall [name ...] [#threads] | Install plugins                                                     |
+| PlugUpdate [name ...] [#threads]  | Install or update plugins                                           |
+| PlugClean[!]                      | Remove unused directories (bang version will clean without prompt)  |
+| PlugUpgrade                       | Upgrade vim-plug itself. You may need to restart Vim after upgrade. |
+| PlugStatus                        | Check the status of plugins                                         |
+| PlugDiff                          | See the updated changes from the previous PlugUpdate                |
 
 ### `Plug` options
 

plug.vim

@@ -544,7 +544,7 @@ function! s:update_impl(pull, force, args) abort
                   \ remove(args, -1) : get(g:, 'plug_threads', 16)
 
   let managed = filter(copy(g:plugs), 's:is_managed(v:key)')
-  let todo = empty(args) ? filter(managed, '!get(v:val, "frozen", 0)') :
+  let todo = empty(args) ? filter(managed, '!v:val.frozen') :
                          \ filter(managed, 'index(args, v:key) >= 0')
 
   if empty(todo)