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/oc_test.go

@@ -0,0 +1,40 @@
+// Copyright 2018 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build go1.8
+
+package bigquery
+
+import (
+	"testing"
+
+	"cloud.google.com/go/internal/testutil"
+	"golang.org/x/net/context"
+)
+
+func TestOCTracing(t *testing.T) {
+	ctx := context.Background()
+	client := getClient(t)
+	defer client.Close()
+
+	te := testutil.NewTestExporter()
+	defer te.Unregister()
+
+	q := client.Query("select *")
+	q.Run(ctx) // Doesn't matter if we get an error; span should be created either way
+
+	if len(te.Spans) == 0 {
+		t.Fatalf("Expected some spans to be created, but got %d", 0)
+	}
+}