Add failing spec for killing and yanking multiple words

GitHub #363

spec/integrations/kill_word_spec.rb

@@ -0,0 +1,14 @@
+describe 'multiple words killed with `backward-kill-word`' do
+  before do
+    session.
+      send_string('echo first second').
+      send_keys('C-w').
+      send_keys('C-w')
+    wait_for { session.content }.to eq('echo')
+  end
+
+  it 'can be yanked back with `yank`' do
+    session.send_keys('C-y')
+    wait_for { session.content }.to eq('echo first second')
+  end
+end