wrap import/test in a rescue block to make it optional

looks like this one was missed in commit: e16bc71590

Signed-off-by: Konstantin Haase <konstantin.mailinglists@googlemail.com>

test/builder_test.rb

@@ -1,4 +1,6 @@
 require File.dirname(__FILE__) + '/helper'
+
+begin
 require 'builder'
 
 class BuilderTest < Test::Unit::TestCase
@@ -87,3 +89,7 @@ class BuilderTest < Test::Unit::TestCase
     assert_raise(Errno::ENOENT) { get('/') }
   end
 end
+
+rescue LoadError
+  warn "#{$!.to_s}: skipping less tests"
+end