[PATCH] Fix variable name with path to rdoc

[Jan Palus]

Patch fixes typo introduced in r1806570 most probably by copy&paste of similar
line searching for ruby binary.

[[[
* configure.ac
  Fix variable name with path to rdoc
]]]
Index: configure.ac
===================================================================
--- configure.ac        (revision 1829148)
+++ configure.ac        (working copy)
@@ -1323,7 +1323,7 @@ if test "$RUBY" != "none"; then
     if test -n "$RDOC"; then
       AC_PATH_PROG(RDOC, "$RDOC", none)
     else
-      AC_PATH_PROGS(RUBY, rdoc rdoc1 rdoc1.8 rdoc18 rdoc1.9 rdoc19 rdoc1.9.3 
rdoc193 rdoc2 rdoc2.0 rdoc20 rdoc2.1 rdoc21 rdoc2.2 rdoc22 rdoc2.3 rdoc23 
rdoc2.4 rdoc24, none)
+      AC_PATH_PROGS(RDOC, rdoc rdoc1 rdoc1.8 rdoc18 rdoc1.9 rdoc19 rdoc1.9.3 
rdoc193 rdoc2 rdoc2.0 rdoc20 rdoc2.1 rdoc21 rdoc2.2 rdoc22 rdoc2.3 rdoc23 
rdoc2.4 rdoc24, none)
     fi
     AC_CACHE_CHECK([for Ruby major version], [svn_cv_ruby_major],[
     svn_cv_ruby_major="`$RUBY -rrbconfig -e 'print 
RbConfig::CONFIG.fetch(%q(MAJOR))'`"