Add missing context value to example (#1373)

`BucketExists` was missing a context value.

We place it in a variable to make the code cleaner.

README.md

@@ -45,7 +45,7 @@ func main() {
 		log.Fatalln(err)
 	}
 
-	log.Printf("%#v\n", minioClient) // minioClient is now setup
+	log.Printf("%#v\n", minioClient) // minioClient is now set up
 }
 ```
 
@@ -67,6 +67,7 @@ import (
 )
 
 func main() {
+	ctx := context.Background()
 	endpoint := "play.min.io"
 	accessKeyID := "Q3AM3UQ867SPQQA43P2F"
 	secretAccessKey := "zuf+tfteSlswRu7BJ86wekitnifILbZam1KYY3TG"
@@ -85,10 +86,10 @@ func main() {
 	bucketName := "mymusic"
 	location := "us-east-1"
 
-	err = minioClient.MakeBucket(context.Background(), bucketName, minio.MakeBucketOptions{Region: location})
+	err = minioClient.MakeBucket(ctx, bucketName, minio.MakeBucketOptions{Region: location})
 	if err != nil {
 		// Check to see if we already own this bucket (which happens if you run this twice)
-		exists, errBucketExists := minioClient.BucketExists(bucketName)
+		exists, errBucketExists := minioClient.BucketExists(ctx, bucketName)
 		if errBucketExists == nil && exists {
 			log.Printf("We already own %s\n", bucketName)
 		} else {
@@ -104,7 +105,7 @@ func main() {
 	contentType := "application/zip"
 
 	// Upload the zip file with FPutObject
-	n, err := minioClient.FPutObject(context.Background(), bucketName, objectName, filePath, minio.PutObjectOptions{ContentType: contentType})
+	n, err := minioClient.FPutObject(ctx, bucketName, objectName, filePath, minio.PutObjectOptions{ContentType: contentType})
 	if err != nil {
 		log.Fatalln(err)
 	}