Add smoke test to check that JSDuck doesn't crash.

A simple check that running jsduck --version results in 0 exit code.

Author: nene

spec/smoke_spec.rb

@@ -0,0 +1,9 @@
+
+describe "smoke test running jsduck --version" do
+
+  it "does not crash" do
+    `./bin/jsduck --version`
+    $?.exitstatus.should == 0
+  end
+
+end