Update sample gem’s Rakefile to make clean/clobber work

Author: tjschuck

sample_gem/Rakefile

@@ -1,6 +1,20 @@
 require"bundler/gem_tasks"
 require"rake/extensiontask"
 require"rake/javaextensiontask"
+require"rake/clean"
+
+CLEAN.include(
+"tmp",
+"lib/1.8",
+"lib/1.9",
+"lib/2.0",
+"lib/2.1",
+"lib/sample_gem_ext.jar",
+"lib/sample_gem_ext.so"
+)
+CLOBBER.include(
+"pkg"
+)
 
 GEMSPEC=Gem::Specification.load(File.expand_path("../sample_gem.gemspec",__FILE__))