Vim compat fix: type variables were introduced in 7.4.2071

To avoid issues for Vim versions between 7.4.1966 and 7.4.2071, we now use
type() to distinguish between the type of variable `job_id` being either Number
or Job.

autoload/sy/repo.vim

@@ -82,7 +82,7 @@ function! sy#repo#get_diff_start(vcs, do_register) abort
 
   " Newer Vim
   elseif v:version > 704 || v:version == 704 && has('patch1967')
-    if job_id is v:t_job
+    if type(job_id) != type(0)
       silent! call job_stop(job_id)
     endif