* apiInvoker : in getInstance, if instance is null initialize instance
build : replace the deprecated volley library by the android one
jsonUtil : Add in gsonBuider an adapter to deserialize Date class
And update petstore sample for volley library
* Update apiInvoker.mustache
Add a space after if, to stick to the code style.
* Update ApiInvoker.java
Add a space after if, in petstore samples, to stick to the code style.
