exampels: indent with spaces on Cassandra example (#88)

Signed-off-by: Calvin Leung Huang <cleung2010@gmail.com>

examples/Cassandra.md

@@ -8,10 +8,10 @@ if err != nil {
 }
 
 options := &dockertest.RunOptions{
-		Repository: "cassandra",
-		Tag:        "latest",
-		Mounts:     []string{"/tmp/local-cassandra:/etc/cassandra"},
-	}
+    Repository: "cassandra",
+    Tag:        "latest",
+    Mounts:     []string{"/tmp/local-cassandra:/etc/cassandra"},
+}
 
 resource, err := pool.RunWithOptions(options)
 if err != nil {
@@ -23,21 +23,21 @@ port, _ := strconv.Atoi(resource.GetPort("9042/tcp"))
 
 // exponential backoff-retry, because the application in the container might not be ready to accept connections yet
 if err := pool.Retry(func() error {
-		clusterConfig := gocql.NewCluster(retURL)
-		clusterConfig.Authenticator = gocql.PasswordAuthenticator{
-			Username: "cassandra",
-			Password: "cassandra",
-		}
-		clusterConfig.ProtoVersion = 4
-		clusterConfig.Port = port
-		log.Printf("%v", clusterConfig.Port)
+    clusterConfig := gocql.NewCluster(retURL)
+    clusterConfig.Authenticator = gocql.PasswordAuthenticator{
+        Username: "cassandra",
+        Password: "cassandra",
+    }
+    clusterConfig.ProtoVersion = 4
+    clusterConfig.Port = port
+    log.Printf("%v", clusterConfig.Port)
 
-		session, err := clusterConfig.CreateSession()
-		if err != nil {
-			return fmt.Errorf("error creating session: %s", err)
-		}
+    session, err := clusterConfig.CreateSession()
+    if err != nil {
+        return fmt.Errorf("error creating session: %s", err)
+    }
     defer session.Close()
-		return nil
+    return nil
 }); err != nil {
     log.Fatalf("Could not connect to docker: %s", err)
 }