The string that you pass into Format needs to be a specific value: 2006-01-02 03:04:05 PM (UTC-7). Notice how you see all the numbers between 1 and 7 in there. The way you define a format in Go is to write that specific date in the format you want to see your actual time value formatted into. In your case, I think you want it to be: "2006.01.02T15:04:05".
The difference is that you used the date 2018-07-08 but it must be the specific date 2006-01-02. Those are magic numbers that Go uses to determine where it should format the year, month and day, respectively.