Add `updated` field on package, rule, and trigger entity (#135)

diff --git a/whisk/package.go b/whisk/package.go
index dcb7e21..a138126 100644
--- a/whisk/package.go
+++ b/whisk/package.go
@@ -46,6 +46,7 @@
 	Binding     *Binding    `json:"binding,omitempty"`
 	Actions     []Action    `json:"actions,omitempty"`
 	Feeds       []Action    `json:"feeds,omitempty"`
+	Updated     int64       `json:"updated,omitempty"`
 }
 
 func (p *Package) GetName() string {
diff --git a/whisk/rule.go b/whisk/rule.go
index 9850948..e52d41f 100644
--- a/whisk/rule.go
+++ b/whisk/rule.go
@@ -39,6 +39,7 @@
 	Trigger     interface{} `json:"trigger"`
 	Action      interface{} `json:"action"`
 	Publish     *bool       `json:"publish,omitempty"`
+	Updated     int64       `json:"updated,omitempty"`
 }
 
 type RuleListOptions struct {
diff --git a/whisk/trigger.go b/whisk/trigger.go
index d4091ae..bda970d 100644
--- a/whisk/trigger.go
+++ b/whisk/trigger.go
@@ -40,6 +40,7 @@
 	Limits       *Limits                `json:"limits,omitempty"`
 	Publish      *bool                  `json:"publish,omitempty"`
 	Rules        map[string]interface{} `json:"rules,omitempty"`
+	Updated      int64                  `json:"updated,omitempty"`
 }
 
 type TriggerListOptions struct {