Use derived-mode-p instead of checking buffer names

Author: phikal

dumb-jump.el

@@ -2112,8 +2112,7 @@ to keep looking for another root."
              (dumb-jump-git-grep-installed?)
              (dumb-jump-grep-installed?)))
     (dumb-jump-issue-result "nogrep"))
-   ((or (string= (buffer-name) "*shell*")
-        (string= (buffer-name) "*eshell*"))
+   ((derived-mode-p 'shell-mode 'eshell-mode)
     (dumb-jump-fetch-shell-results prompt))
    ((and (not prompt) (not (region-active-p)) (not (thing-at-point 'symbol)))
     (dumb-jump-issue-result "nosymbol"))