fix: utcOffset, when offset has minutes <> '0' or '30'

Example for offset not full or halve hours is '1879-12-31' for
timezone 'Europe/Berlin', where utcOffset is '00:53'.
Solves issue iamkun#1996.

README.md

@@ -11,6 +11,7 @@
   - accessing get / set with unit string (e.g. "`dayjs().get('year')`") takes short form of units too (allowed values are 'y', 'M', 'D', 'h', 'm', 's', 'ms').
   - unlike 'moment': Day of Week is accessible by name ('D' / 'day') too.
   - unlike 'moment': the **unit names are case sensitive**.
+  - make utcOffset() behave like 'moment' (rounding away only the fractional part of the minutes - i.e. the seconds - and not the minutes to a quarter of an hour).
 
 ---
 

src/dayjs.ts

@@ -380,9 +380,8 @@ export class Dayjs extends (class {} as Extend) {
   }
 
   utcOffset() {
-    // Because a bug at FF24, we're rounding the timezone offset around 15 minutes
-    // https://github.com/moment/moment/pull/1871
-    return -Math.round(this._d.getTimezoneOffset() / 15) * 15
+    // Remove fractional part (seconds) from offset (just like moment.js does)
+    return -Math.round(this._d.getTimezoneOffset())
   }
 
   format(formatStr?: string) {