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/drive/v2/drive-api.json

@@ -38,7 +38,7 @@
   "description": "Manages files in Drive including uploading, downloading, searching, detecting changes, and updating sharing permissions.",
   "discoveryVersion": "v1",
   "documentationLink": "https://developers.google.com/drive/",
-  "etag": "\"-iA1DTNe4s-I6JZXPt1t1Ypy8IU/3sZY5SudRICrZaNsZzXj7Gt8kVY\"",
+  "etag": "\"Zkyw9ACJZUvcYmlFaKGChzhmtnE/f5YU4B1YgiNFEadOJN80qPxEFqA\"",
   "icons": {
     "x16": "https://ssl.gstatic.com/docs/doclist/images/drive_icon_16.png",
     "x32": "https://ssl.gstatic.com/docs/doclist/images/drive_icon_32.png"
@@ -83,12 +83,12 @@
       "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"
     }
@@ -2331,7 +2331,7 @@
           ]
         },
         "patch": {
-          "description": "Updates a property, or adds it if it doesn't exist. This method supports patch semantics.",
+          "description": "Updates a property.",
           "httpMethod": "PATCH",
           "id": "drive.properties.patch",
           "parameterOrder": [
@@ -2353,7 +2353,7 @@
             },
             "visibility": {
               "default": "private",
-              "description": "The visibility of the property.",
+              "description": "The visibility of the property. Allowed values are PRIVATE and PUBLIC. (Default: PRIVATE)",
               "location": "query",
               "type": "string"
             }
@@ -2373,7 +2373,7 @@
           ]
         },
         "update": {
-          "description": "Updates a property, or adds it if it doesn't exist.",
+          "description": "Updates a property.",
           "httpMethod": "PUT",
           "id": "drive.properties.update",
           "parameterOrder": [
@@ -2395,7 +2395,7 @@
             },
             "visibility": {
               "default": "private",
-              "description": "The visibility of the property.",
+              "description": "The visibility of the property. Allowed values are PRIVATE and PUBLIC. (Default: PRIVATE)",
               "location": "query",
               "type": "string"
             }
@@ -3074,7 +3074,7 @@
       }
     }
   },
-  "revision": "20180209",
+  "revision": "20180413",
   "rootUrl": "https://www.googleapis.com/",
   "schemas": {
     "About": {
@@ -4750,6 +4750,11 @@
           "type": "string"
         },
         "key": {
+          "annotations": {
+            "required": [
+              "drive.properties.insert"
+            ]
+          },
           "description": "The key of this property.",
           "type": "string"
         },
@@ -4767,7 +4772,7 @@
           "type": "string"
         },
         "visibility": {
-          "description": "The visibility of this property.",
+          "description": "The visibility of this property. Allowed values are PRIVATE and PUBLIC. (Default: PRIVATE)",
           "type": "string"
         }
       },