scanner: fix indent error for line comment generated by vdoc

[yuyi98]

This PR fix indent error for line comment generated by vdoc.

before:

yuyi@yuyi-PC:~$ v doc time
module time

const (
        days_string        = 'MonTueWedThuFriSatSun'
        long_days          = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday',
                'Sunday']
        month_days         = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
        months_string      = 'JanFebMarAprMayJunJulAugSepOctNovDec'
        long_months        = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August',
                'September', 'October', 'November', 'December']
// The unsigned zero year for internal calculations.
// Must be 1 mod 400, and times before it will not compute correctly,
// but otherwise can be changed at will.
        absolute_zero_year = i64(-292277022399)
        seconds_per_minute = 60
        seconds_per_hour   = 60 * seconds_per_minute
        seconds_per_day    = 24 * seconds_per_hour
        seconds_per_week   = 7 * seconds_per_day
        days_per_400_years = days_in_year * 400 + 97
        days_per_100_years = days_in_year * 100 + 24
        days_per_4_years   = days_in_year * 4 + 1
        days_in_year       = 365
...

now:

PS D:\Vlang\v> v doc time
module time

const (
        days_string        = 'MonTueWedThuFriSatSun'
        long_days          = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday',
                'Sunday']
        month_days         = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
        months_string      = 'JanFebMarAprMayJunJulAugSepOctNovDec'
        long_months        = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August',
                'September', 'October', 'November', 'December']
        // The unsigned zero year for internal calculations.
        // Must be 1 mod 400, and times before it will not compute correctly,
        // but otherwise can be changed at will.
        absolute_zero_year = i64(-292277022399)
        seconds_per_minute = 60
        seconds_per_hour   = 60 * seconds_per_minute
        seconds_per_day    = 24 * seconds_per_hour
        seconds_per_week   = 7 * seconds_per_day
        days_per_400_years = days_in_year * 400 + 97
        days_per_100_years = days_in_year * 100 + 24
        days_per_4_years   = days_in_year * 4 + 1
        days_in_year       = 365
        days_before        = [