fix: do not depend on test host timezone

Author: achingbrain

test/files/format-mtime.spec.js

@@ -10,10 +10,10 @@ const expect = chai.expect
 
 describe('format-mtime', function () {
   it('formats mtime', function () {
-    expect(formatMtime({ secs: 100, nsecs: 0 })).to.equal('Jan 1, 1970, 1:01:40 AM GMT+1')
+    expect(formatMtime({ secs: 100, nsecs: 0 })).to.include('Jan 1, 1970')
   })
 
   it('formats empty mtime', function () {
-    expect(formatMtime()).to.equal('Jan 1, 1970, 1:00:00 AM GMT+1')
+    expect(formatMtime()).to.include('Jan 1, 1970')
   })
 })