rbinstall.rb: literal colon

* tool/rbinstall.rb (PROLOG_SCRIPT): ":" in "Use Alternate Value"
  parameter expansion is not a path separator, but a literal colon.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49436 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/rbinstall.rb

@@ -424,7 +424,7 @@ EOS
     pathsep = File::PATH_SEPARATOR
     PROLOG_SCRIPT << <<EOS
 prefix="${bindir%/bin}"
-export #{libpathenv}="$prefix/lib${#{libpathenv}#{pathsep}+#{pathsep}$#{libpathenv}}"
+export #{libpathenv}="$prefix/lib${#{libpathenv}:+#{pathsep}$#{libpathenv}}"
 EOS
   end
   PROLOG_SCRIPT << %Q[exec "$bindir/#{ruby_install_name}" -x "$0" "$@"\n]