Fix use of minted with beamer export

* lisp/org-beamer.el: Mark frame as fragile when it is using minted
for src block export.

lisp/org-beamer.el

@@ -399,7 +399,7 @@ the value will be inserted right after the documentclass statement."
       (insert org-beamer-header-extra)
       (or (bolp) (insert "\n"))))))
 
-(defcustom org-beamer-fragile-re "^[ \t]*\\\\begin{\\(verbatim\\|lstlisting\\)}"
+(defcustom org-beamer-fragile-re "^[ \t]*\\\\begin{\\(verbatim\\|lstlisting\\|minted\\)}"
   "If this regexp matches in a frame, the frame is marked as fragile."
   :group 'org-beamer
   :type 'regexp)