vendor: update all dependencies

* Update all dependencies
  * Remove all `[[constraint]]` from Gopkg.toml
  * Add in the minimum number of `[[override]]` to build
  * Remove go get of github.com/inconshreveable/mousetrap as it is vendored
  * Update docs with new policy on constraints

vendor/google.golang.org/api/calendar/v3/calendar-api.json

@@ -17,7 +17,7 @@
   "description": "Manipulates events and other calendar data.",
   "discoveryVersion": "v1",
   "documentationLink": "https://developers.google.com/google-apps/calendar/firstapp",
-  "etag": "\"-iA1DTNe4s-I6JZXPt1t1Ypy8IU/yCy5sb24vtyNhrLP2aRyDfx5GsY\"",
+  "etag": "\"Zkyw9ACJZUvcYmlFaKGChzhmtnE/1VOFhc7FcQH_8hh6rAZ7o3yjhp8\"",
   "icons": {
     "x16": "http://www.google.com/images/icons/product/calendar-16.png",
     "x32": "http://www.google.com/images/icons/product/calendar-32.png"
@@ -62,12 +62,12 @@
       "type": "boolean"
     },
     "quotaUser": {
-      "description": "Available to use for quota purposes for server-side applications. Can be any arbitrary string assigned to a user, but should not exceed 40 characters. Overrides userIp if both are provided.",
+      "description": "An opaque string that represents a user for quota purposes. Must not exceed 40 characters.",
       "location": "query",
       "type": "string"
     },
     "userIp": {
-      "description": "IP address of the site where the request originates. Use this if you want to enforce per-user limits.",
+      "description": "Deprecated. Please use quotaUser instead.",
       "location": "query",
       "type": "string"
     }
@@ -1604,7 +1604,7 @@
       }
     }
   },
-  "revision": "20180130",
+  "revision": "20180424",
   "rootUrl": "https://www.googleapis.com/",
   "schemas": {
     "Acl": {
@@ -2566,7 +2566,7 @@
         },
         "resource": {
           "default": "false",
-          "description": "Whether the attendee is a resource. Read-only. The default is False.",
+          "description": "Whether the attendee is a resource. Can only be set when the attendee is added to the event for the first time. Subsequent modifications are ignored. Optional. The default is False.",
           "type": "boolean"
         },
         "responseStatus": {

vendor/google.golang.org/api/calendar/v3/calendar-gen.go

@@ -1747,8 +1747,9 @@ type EventAttendee struct {
 	// Read-only. The default is False.
 	Organizer bool `json:"organizer,omitempty"`
 
-	// Resource: Whether the attendee is a resource. Read-only. The default
-	// is False.
+	// Resource: Whether the attendee is a resource. Can only be set when
+	// the attendee is added to the event for the first time. Subsequent
+	// modifications are ignored. Optional. The default is False.
 	Resource bool `json:"resource,omitempty"`
 
 	// ResponseStatus: The attendee's response status. Possible values are: