Upgrade dependencies to latest weaveworks/common.

Commands run:
```
$ gvt delete github.com/weaveworks/common
$ gvt fetch -revision 59b2b6f8dad04cc1e3538885ddf4ed832095295d github.com/weaveworks/common
```
N.B.: following this commit, build fails with:
```
vendor/github.com/docker/docker/pkg/archive/archive.go:19:2: cannot find package "github.com/docker/docker/pkg/fileutils" in any of:
	/go/src/github.com/weaveworks/scope/vendor/github.com/docker/docker/vendor/github.com/docker/docker/pkg/fileutils (vendor tree)
	/go/src/github.com/weaveworks/scope/vendor/github.com/docker/docker/pkg/fileutils
	/usr/local/go/src/github.com/docker/docker/pkg/fileutils (from $GOROOT)
	/go/src/github.com/docker/docker/pkg/fileutils (from $GOPATH)
vendor/github.com/fsouza/go-dockerclient/client.go:35:2: cannot find package "github.com/docker/docker/pkg/stdcopy" in any of:
	/go/src/github.com/weaveworks/scope/vendor/github.com/docker/docker/pkg/stdcopy (vendor tree)
	/usr/local/go/src/github.com/docker/docker/pkg/stdcopy (from $GOROOT)
	/go/src/github.com/docker/docker/pkg/stdcopy (from $GOPATH)
```
Resolution in subsequent commit.

vendor/github.com/go-kit/kit/log/nop_logger.go

+package log
+
+type nopLogger struct{}
+
+// NewNopLogger returns a logger that doesn't do anything.
+func NewNopLogger() Logger { return nopLogger{} }
+
+func (nopLogger) Log(...interface{}) error { return nil }

vendor/github.com/go-kit/kit/log/term/colorwriter_others.go

+// +build !windows
+
+package term
+
+import "io"
+
+// NewColorWriter returns an io.Writer that writes to w and provides cross
+// platform support for ANSI color codes. If w is not a terminal it is
+// returned unmodified.
+func NewColorWriter(w io.Writer) io.Writer {
+	return w
+}

vendor/github.com/go-kit/kit/log/term/term.go

+// Package term provides tools for logging to a terminal.
+package term
+
+import (
+	"io"
+
+	"github.com/go-kit/kit/log"
+)
+
+// NewLogger returns a Logger that takes advantage of terminal features if
+// possible. Log events are formatted by the Logger returned by newLogger. If
+// w is a terminal each log event is colored according to the color function.
+func NewLogger(w io.Writer, newLogger func(io.Writer) log.Logger, color func(keyvals ...interface{}) FgBgColor) log.Logger {
+	if !IsTerminal(w) {
+		return newLogger(w)
+	}
+	return NewColorLogger(NewColorWriter(w), newLogger, color)
+}
+
+type fder interface {
+	Fd() uintptr
+}

vendor/github.com/go-kit/kit/log/term/terminal_darwin.go

+// Based on ssh/terminal:
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package term
+
+import "syscall"
+
+const ioctlReadTermios = syscall.TIOCGETA