all: use stdlib context instead of x/net/context

This PR replaces use of `x/net/context` with the standard `context`

It has been nearly 6 months since
https://github.com/golang/oauth2/issues/246#issuecomment-387601277 so
I made this PR so it will be ready to merge when needed (and if
possible).

Fixes #246

Change-Id: Id2c316fcb27de0fb9163ceb4e8669b04cb39a987
GitHub-Last-Rev: 5b36321dccef8da97d67188fe307d1c135793ad6
GitHub-Pull-Request: golang/oauth2#339
Reviewed-on: https://go-review.googlesource.com/c/145202
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

google/appengine.go

@@ -5,9 +5,9 @@
 package google
 
 import (
+	"context"
 	"time"
 
-	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 )
 

google/default.go

@@ -5,6 +5,7 @@
 package google
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
@@ -14,7 +15,6 @@ import (
 	"runtime"
 
 	"cloud.google.com/go/compute/metadata"
-	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 )
 

google/example_test.go

@@ -5,12 +5,12 @@
 package google_test
 
 import (
+	"context"
 	"fmt"
 	"io/ioutil"
 	"log"
 	"net/http"
 
-	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	"golang.org/x/oauth2/jwt"

google/go19.go

@@ -7,7 +7,8 @@
 package google
 
 import (
-	"golang.org/x/net/context"
+	"context"
+
 	"golang.org/x/oauth2"
 )
 

google/google.go

@@ -5,6 +5,7 @@
 package google
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -12,7 +13,6 @@ import (
 	"time"
 
 	"cloud.google.com/go/compute/metadata"
-	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/jwt"
 )

google/not_go19.go

@@ -7,7 +7,8 @@
 package google
 
 import (
-	"golang.org/x/net/context"
+	"context"
+
 	"golang.org/x/oauth2"
 )
 

google/sdk.go

@@ -6,6 +6,7 @@ package google
 
 import (
 	"bufio"
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -18,7 +19,6 @@ import (
 	"strings"
 	"time"
 
-	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 )