start the web3 service for the build task so that contracts can be deployed

lib/index.js

@@ -143,7 +143,8 @@ var Embark = (function () {
         if (pluginList.length > 0) {
           engine.logger.info("loaded plugins: " + pluginList.join(", "));
         }
-
+        
+        engine.startService("web3");
         engine.startService("pipeline");
         engine.startService("abi");
         engine.startService("deployment");