Catch :task_has_failed on the cli. (Fixes #88)

Since the server throws the Guard symbol :task_has_failed
to exit quickly, the cli wasn't catching it at all, leading to an
abrupt process termination and leaving the server running.

Now that :task_has_failed is catched, the cli runner tries to
run the specs anyway and terminates the server properly if
the runner is not available.

lib/guard/jasmine/cli.rb

@@ -123,7 +123,9 @@ def spec(*paths)
         runner_options[:max_error_notify] = 0
 
         if CLI.phantomjs_bin_valid?(runner_options[:phantomjs_bin])
-          ::Guard::Jasmine::Server.start(runner_options) unless runner_options[:server] == :none
+          catch (:task_has_failed) do
+            ::Guard::Jasmine::Server.start(runner_options) unless runner_options[:server] == :none
+          end
 
           if CLI.runner_available?(runner_options)
             result = ::Guard::Jasmine::Runner.run(paths, runner_options)