code health: unify messages format in datetime examples

After the patch all messages in datetime/example_test.go start with
a capital letter.

Author: oleg-jukovec

datetime/example_test.go

@@ -25,14 +25,14 @@ func Example() {
 	}
 	conn, err := tarantool.Connect("127.0.0.1:3013", opts)
 	if err != nil {
-		fmt.Printf("error in connect is %v", err)
+		fmt.Printf("Error in connect is %v", err)
 		return
 	}
 
 	var datetime = "2013-10-28T17:51:56.000000009Z"
 	tm, err := time.Parse(time.RFC3339, datetime)
 	if err != nil {
-		fmt.Printf("error in time.Parse() is %v", err)
+		fmt.Printf("Error in time.Parse() is %v", err)
 		return
 	}
 	dt, err := NewDatetime(tm)
@@ -47,7 +47,7 @@ func Example() {
 	// Replace a tuple with datetime.
 	resp, err := conn.Replace(space, []interface{}{dt})
 	if err != nil {
-		fmt.Printf("error in replace is %v", err)
+		fmt.Printf("Error in replace is %v", err)
 		return
 	}
 	respDt := resp.Data[0].([]interface{})[0].(Datetime)
@@ -60,7 +60,7 @@ func Example() {
 	var limit uint32 = 1
 	resp, err = conn.Select(space, index, offset, limit, tarantool.IterEq, []interface{}{dt})
 	if err != nil {
-		fmt.Printf("error in select is %v", err)
+		fmt.Printf("Error in select is %v", err)
 		return
 	}
 	respDt = resp.Data[0].([]interface{})[0].(Datetime)
@@ -71,7 +71,7 @@ func Example() {
 	// Delete a tuple with datetime.
 	resp, err = conn.Delete(space, index, []interface{}{dt})
 	if err != nil {
-		fmt.Printf("error in delete is %v", err)
+		fmt.Printf("Error in delete is %v", err)
 		return
 	}
 	respDt = resp.Data[0].([]interface{})[0].(Datetime)