fix(cli): allow running from command line without a config file

If all necessary fields are specified (e.g. seleniumAddress and at least
one spec), a config file shouldn't be necessary.

Author: juliemr

lib/cli.js

@@ -251,7 +251,11 @@ while(args.length) {
   }
 }
 
-merge(config, require(configPath).config);
+if (configPath) {
+  merge(config, require(configPath).config);
+} else {
+  configDir = "./";
+}
 merge(config, commandLineConfig);
 
 var sauceAccount;