Drop support for hub

You can still enable this manually with

    let g:fugitive_git_command = 'hub'

But Fugitive will likely be dropping support for that in the future.

README.markdown

@@ -5,9 +5,6 @@ of features:
 
 * Enables `:GBrowse` from fugitive.vim to open GitHub URLs.
 
-* Sets up `:Git` to use [`hub`](https://github.com/github/hub) if installed
-  rather than `git`.
-
 * In commit messages, GitHub issues, issue URLs, and collaborators can be
   omni-completed (`<C-X><C-O>`, see `:help compl-omni`).  This makes inserting
   those `Closes #123` remarks slightly easier than copying and pasting from
@@ -45,6 +42,19 @@ If you are using GitHub Enterprise, repeat this step for each domain (omit the
 
     set completeopt-=preview
 
+> What happened to the support for [`hub`](https://github.com/github/hub)?
+
+Support was dropped partially because [GitHub CLI](https://github.com/cli/cli)
+appears to be unseating it as the preferred GitHub command line solution, and
+partly because `hub` isn't quite a perfect drop-in replacement for `git`,
+making life more difficult for Fugitive.  My recommended solution is to call
+it via a Git alias:
+
+    git config --global alias.hub '!hub'
+
+This will let you call `hub pull-request` via `:Git hub pull-request`, for
+example.
+
 ## Self-Promotion
 
 Like rhubarb.vim? Follow the repository on

plugin/rhubarb.vim

@@ -11,10 +11,6 @@ if !exists('g:dispatch_compilers')
 endif
 let g:dispatch_compilers['hub'] = 'git'
 
-if !exists('g:fugitive_git_command') && executable('hub')
-  let g:fugitive_git_command = 'hub'
-endif
-
 function! s:Config() abort
   if exists('*FugitiveFind')
     let dir = FugitiveFind('.git/config')[0:-8]