Fix logrus package import case

The logrus package import changed letter case:
sirupsen/logrus#384

In c31b012 I opted to use the same case as Prometheus packages I depend
on to avoid case conflicts.

I'm about to start using Go's dep tool for dependency management, and
the old logrus import prevents dep from completing its initialisation
because newer Prometheus packages use the lowercase import path:
golang/dep#797

Use the lowercase import path for consistency with the Prometheus
packages.

cmd/athensdb/main.go

@@ -8,7 +8,6 @@ import (
 	"os"
 	"time"
 
-	log "github.com/Sirupsen/logrus"
 	v1API "github.com/mattbostock/athensdb/internal/api/v1"
 	"github.com/mattbostock/athensdb/internal/cluster"
 	"github.com/mattbostock/athensdb/internal/write"
@@ -17,6 +16,7 @@ import (
 	"github.com/prometheus/common/route"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/storage/tsdb"
+	log "github.com/sirupsen/logrus"
 	"golang.org/x/net/context"
 	"gopkg.in/alecthomas/kingpin.v2"
 )

internal/cluster/cluster.go

@@ -9,9 +9,9 @@ import (
 	"strconv"
 	"time"
 
-	"github.com/Sirupsen/logrus"
 	"github.com/golang/groupcache/consistenthash"
 	"github.com/hashicorp/memberlist"
+	"github.com/sirupsen/logrus"
 )
 
 const (

internal/write/write.go

@@ -10,13 +10,13 @@ import (
 	"sync"
 	"time"
 
-	"github.com/Sirupsen/logrus"
 	"github.com/golang/protobuf/proto"
 	"github.com/golang/snappy"
 	"github.com/mattbostock/athensdb/internal/cluster"
 	"github.com/mattbostock/athensdb/internal/remote"
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/storage"
+	"github.com/sirupsen/logrus"
 	"golang.org/x/net/context/ctxhttp"
 )