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/cloud.google.com/go/bigquery/bigquery.go

@@ -47,6 +47,11 @@ func setClientHeader(headers http.Header) {
 
 // Client may be used to perform BigQuery operations.
 type Client struct {
+	// Location, if set, will be used as the default location for all subsequent
+	// dataset creation and job operations. A location specified directly in one of
+	// those operations will override this value.
+	Location string
+
 	projectID string
 	bqs       *bq.Service
 }