Fix malformed create command

`omitempty` doesn't cover sub-structs, so we were passing in:

{"name":"omgwtfapp","region":{}}

API recently changed the format for identifiers to be just a string
instead of a nested object. So it's now `"region": "eu"`.

Fixes #85.

create.go

@@ -22,11 +22,9 @@ func runCreate(cmd *Command, args []string) {
 	var app App
 	var v struct {
 		Name   string `json:"name,omitempty"`
-		Region struct {
-			Name string `json:"name,omitempty"`
-		} `json:"region,omitempty"`
+		Region string `json:"region,omitempty"`
 	}
-	v.Region.Name = flagRegion
+	v.Region = flagRegion
 	if len(args) > 0 {
 		v.Name = args[0]
 	}