fix poll plugin specs deprecations

plugins/poll/spec/poll_plugin/poll_spec.rb

@@ -7,20 +7,20 @@ describe PollPlugin::Poll do
   let(:user) { Fabricate(:user) }
 
   it "should detect poll post correctly" do
-    expect(poll.is_poll?).should == true
+    expect(poll.is_poll?).to be_truthy
     post2 = create_post(topic: topic, raw: "This is a generic reply.")
-    expect(PollPlugin::Poll.new(post2).is_poll?).should == false
+    expect(PollPlugin::Poll.new(post2).is_poll?).to be_falsey
     post.topic.title = "Not a poll"
-    expect(poll.is_poll?).should == false
+    expect(poll.is_poll?).to be_falsey
   end
 
   it "strips whitespace from the prefix translation" do
     topic.title = "Polll: This might be a poll"
     topic.save
-    expect(PollPlugin::Poll.new(post).is_poll?).should == false
+    expect(PollPlugin::Poll.new(post).is_poll?).to be_falsey
     I18n.expects(:t).with('poll.prefix').returns("Polll ")
     I18n.expects(:t).with('poll.closed_prefix').returns("Closed Poll ")
-    expect(PollPlugin::Poll.new(post).is_poll?).should == true
+    expect(PollPlugin::Poll.new(post).is_poll?).to be_truthy
   end
 
   it "should get options correctly" do