Add a build info metric (#323)

* Add a build info metric

Add a standard Prometheus build info metric to make monitoring rollouts
easier.

* Update prometheus vendoring.

* Fix build error

Fix missing bool in builtinMetricMaps.

Signed-off-by: Ben Kochie <superq@gmail.com>

vendor/github.com/prometheus/procfs/proc_limits.go

@@ -1,3 +1,16 @@
+// Copyright 2018 The Prometheus Authors
+// 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.
+
 package procfs
 
 import (
@@ -65,7 +78,14 @@ var (
 )
 
 // NewLimits returns the current soft limits of the process.
+//
+// Deprecated: use p.Limits() instead
 func (p Proc) NewLimits() (ProcLimits, error) {
+	return p.Limits()
+}
+
+// Limits returns the current soft limits of the process.
+func (p Proc) Limits() (ProcLimits, error) {
 	f, err := os.Open(p.path("limits"))
 	if err != nil {
 		return ProcLimits{}, err