ox-beamer: Update default environment templates

* lisp/ox-beamer.el (org-beamer-environments-default): Update
  templates wrt %U.

%U meaning changed in commit
 f3168ff90a22f8514abf99c1052e828174ff17a8 (June 2013) but the variable
 wasn't updated accordingly.

lisp/ox-beamer.el

@@ -174,11 +174,11 @@ through `org-beamer-environments-extra' variable.")
     ("quotation"      "q" "\\begin{quotation}%a %% %h"    "\\end{quotation}")
     ("quote"          "Q" "\\begin{quote}%a %% %h"        "\\end{quote}")
     ("structureenv"   "s" "\\begin{structureenv}%a %% %h" "\\end{structureenv}")
-    ("theorem"        "t" "\\begin{theorem}%a%U"          "\\end{theorem}")
-    ("definition"     "d" "\\begin{definition}%a%U"       "\\end{definition}")
-    ("example"        "e" "\\begin{example}%a%U"          "\\end{example}")
+    ("theorem"        "t" "\\begin{theorem}%a[%h]"        "\\end{theorem}")
+    ("definition"     "d" "\\begin{definition}%a[%h]"     "\\end{definition}")
+    ("example"        "e" "\\begin{example}%a[%h]"        "\\end{example}")
     ("exampleblock"   "E" "\\begin{exampleblock}%a{%h}"   "\\end{exampleblock}")
-    ("proof"          "p" "\\begin{proof}%a%U"            "\\end{proof}")
+    ("proof"          "p" "\\begin{proof}%a[%h]"          "\\end{proof}")
     ("beamercolorbox" "o" "\\begin{beamercolorbox}%o{%h}" "\\end{beamercolorbox}"))
   "Environments triggered by properties in Beamer export.
 These are the defaults - for user definitions, see