BUGFIX: LOC record latitude/longitude overflow on 32 bit archs

[al20ov]

The 045-loc.js test fails for me on i686:

--- FAIL: TestParsedFiles (0.55s)
    --- FAIL: TestParsedFiles/045-loc.js (0.02s)
        js_test.go:51: json: cannot unmarshal number -2403461648 into Go struct field DomainConfig.domains.records.loclongitude of type int
FAIL
FAIL	github.com/StackExchange/dnscontrol/v4/pkg/js	0.553s
FAIL

So in pkg/js/helpers.js, I found out that the bit shift operator always returns a signed int32 which means 1 << 31 evaluates to -2147483648 whereas Math.pow(2, 31) gives the correct value of +2147483648 for the equator and prime meridian.

And in models/record.go, LocLatitude and LocLongitude in UnmarshalJSON were typed as int which didn't match the main struct or RFC 1876 apparently and on 32 bit architectures, int ends up as a signed 32 bit integer and any lat/lon coordinates north of the equator or east of the prime meridian can overflow that which causes json.Unmarshal to fail.