Fail with an error if node is not installed when running rake spec

Rakefile

@@ -33,7 +33,7 @@ task :spec => ["spec:node", "spec:browser", "jasmine:hint"]
 namespace :spec do
   desc 'Run specs in Node.js'
   task :node do
-    system("node spec/node_suite.js")
+    raise "Node is required to run all jasmine specs" unless system("node spec/node_suite.js")
   end
 
   desc "Run specs in the default browser (MacOS only)"
@@ -163,4 +163,4 @@ jasmine.version_= {
     exec "cd #{temp_dir} && zip -r #{zip_file_name} . -x .[a-zA-Z0-9]*"
   end
 
-end
+end