Switch to base context package

Change-Id: Iab145a095306252eafedcdab005fb4c71e2815c6
diff --git a/api.go b/api.go
index 0a8c8f8..1f326ae 100644
--- a/api.go
+++ b/api.go
@@ -15,11 +15,10 @@
 package zoekt
 
 import (
+	"context"
 	"fmt"
 	"time"
 
-	"golang.org/x/net/context"
-
 	"github.com/google/zoekt/query"
 )
 
diff --git a/cmd/zoekt-test/main.go b/cmd/zoekt-test/main.go
index 01b2efa..6bc3664 100644
--- a/cmd/zoekt-test/main.go
+++ b/cmd/zoekt-test/main.go
@@ -18,6 +18,7 @@
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"flag"
 	"fmt"
 	"io/ioutil"
@@ -28,8 +29,6 @@
 	"sort"
 	"strings"
 
-	"golang.org/x/net/context"
-
 	"github.com/google/zoekt"
 	"github.com/google/zoekt/build"
 	"github.com/google/zoekt/query"
diff --git a/cmd/zoekt/main.go b/cmd/zoekt/main.go
index 6e68f05..27fd1c2 100644
--- a/cmd/zoekt/main.go
+++ b/cmd/zoekt/main.go
@@ -15,6 +15,7 @@
 package main
 
 import (
+	"context"
 	"flag"
 	"fmt"
 	"log"
@@ -22,8 +23,6 @@
 	"path/filepath"
 	"runtime/pprof"
 
-	"golang.org/x/net/context"
-
 	"github.com/google/zoekt"
 	"github.com/google/zoekt/query"
 	"github.com/google/zoekt/shards"
diff --git a/eval.go b/eval.go
index 15c6137..e4909c4 100644
--- a/eval.go
+++ b/eval.go
@@ -15,6 +15,7 @@
 package zoekt
 
 import (
+	"context"
 	"fmt"
 	"log"
 	"regexp"
@@ -22,8 +23,6 @@
 	"strings"
 	"unicode/utf8"
 
-	"golang.org/x/net/context"
-
 	"github.com/google/zoekt/query"
 )
 
diff --git a/index_test.go b/index_test.go
index 196a300..02b9134 100644
--- a/index_test.go
+++ b/index_test.go
@@ -16,6 +16,7 @@
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"log"
 	"reflect"
@@ -26,7 +27,6 @@
 	"unicode/utf8"
 
 	"github.com/kylelemons/godebug/pretty"
-	"golang.org/x/net/context"
 
 	"github.com/google/zoekt/query"
 )
diff --git a/shards/shards.go b/shards/shards.go
index 2abaf57..a74f4ee 100644
--- a/shards/shards.go
+++ b/shards/shards.go
@@ -15,14 +15,13 @@
 package shards
 
 import (
+	"context"
 	"log"
 	"runtime"
 	"runtime/debug"
 	"sort"
 	"time"
 
-	"golang.org/x/net/context"
-
 	"github.com/google/zoekt"
 	"github.com/google/zoekt/query"
 )
diff --git a/shards/shards_test.go b/shards/shards_test.go
index cfa2d5b..03dd37a 100644
--- a/shards/shards_test.go
+++ b/shards/shards_test.go
@@ -16,12 +16,11 @@
 
 import (
 	"bytes"
+	"context"
 	"log"
 	"os"
 	"testing"
 
-	"golang.org/x/net/context"
-
 	"github.com/google/zoekt"
 	"github.com/google/zoekt/query"
 )
diff --git a/web/e2e_test.go b/web/e2e_test.go
index 4680cb5..a9ad263 100644
--- a/web/e2e_test.go
+++ b/web/e2e_test.go
@@ -16,6 +16,7 @@
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"io/ioutil"
 	"log"
@@ -27,7 +28,6 @@
 
 	"github.com/google/zoekt"
 	"github.com/google/zoekt/query"
-	"golang.org/x/net/context"
 )
 
 const jsonContentType = "application/json; charset=utf-8"