Prevent RI Driver test from loading ~/.rdoc

On ruby 1.8 this will fail as the ri data contains references to
Encoding which is not present.

Author: drbrain

test/test_rdoc_ri_driver.rb

@@ -939,7 +939,10 @@ def test_formatter
     tty = Object.new
     def tty.tty?() true; end
 
-    driver = RDoc::RI::Driver.new
+    @options.delete :use_stdout
+    @options.delete :formatter
+
+    driver = RDoc::RI::Driver.new @options
 
     assert_instance_of @RM::ToAnsi, driver.formatter(tty)