spanner/spansql: the format of the timestamp literal is invalid

[neglect-yp]

(tl TimestampLiteral) SQL() generates a timestamp literal like TIMESTAMP '2014-09-27 12:34:56.123456 -07:00' now.

google-cloud-go/spanner/spansql/sql.go

Line 739 in 9d22bec

fmt.Fprintf(sb, "TIMESTAMP '%s'", time.Time(tl).Format("2006-01-02 15:04:05.000000 -07:00"))

google-cloud-go/spanner/spansql/sql_test.go

Line 559 in 9d22bec

`TIMESTAMP '2014-09-27 12:34:56.123456 -07:00'`,

However, this format is not allowed in the real spanner. I tested this issue using https://github.com/cloudspannerecosystem/spanner-cli and web console.

spanner> SELECT TIMESTAMP '2014-09-27 12:34:56.123456 -07:00';
ERROR: spanner: code = "InvalidArgument", desc = "Invalid TIMESTAMP literal [at 1:8]\\nSELECT TIMESTAMP \\'2014-09-27 12:34:56.123456 -07:00\\'\\n       ^"
spanner> SELECT TIMESTAMP '2014-09-27 12:34:56.123456-07:00';
+-----------------------------+
|                             |
+-----------------------------+
| 2014-09-27T19:34:56.123456Z |
+-----------------------------+
1 rows in set (1.11 msecs)

[neglect-yp]

I'll create a PR for this issue.