Bugfix: Updates Diff Hashes (#106)

Rather than using branch names we are using the hashes provided directly in the Gitlab API response, to compare the point at which the branch diverged from the target to the head commit. We are additionally flashing a warning if the MR contains a merge conflict.

lua/gitlab/job.lua

@@ -22,6 +22,9 @@ M.run_job = function(endpoint, method, body, callback)
     args = args,
     on_stdout = function(_, output)
       vim.defer_fn(function()
+        if output == nil then
+          return
+        end
         local data_ok, data = pcall(vim.json.decode, output)
         if not data_ok then
           local msg = string.format("Failed to parse JSON from %s endpoint", endpoint)