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/youtubereporting/v1/youtubereporting-api.json

@@ -420,7 +420,7 @@
       }
     }
   },
-  "revision": "20180203",
+  "revision": "20180326",
   "rootUrl": "https://youtubereporting.googleapis.com/",
   "schemas": {
     "Empty": {
@@ -752,7 +752,6 @@
           "type": "string"
         },
         "isPotentialRetry": {
-          "default": "true",
           "description": "gdata",
           "type": "boolean"
         },

vendor/google.golang.org/api/youtubereporting/v1/youtubereporting-gen.go

@@ -548,9 +548,7 @@ type GdataMedia struct {
 	Inline string `json:"inline,omitempty"`
 
 	// IsPotentialRetry: gdata
-	//
-	// Default: true
-	IsPotentialRetry *bool `json:"isPotentialRetry,omitempty"`
+	IsPotentialRetry bool `json:"isPotentialRetry,omitempty"`
 
 	// Length: gdata
 	Length int64 `json:"length,omitempty,string"`