fix: correct checking of the number.unsigned flag

Issue #251

src/number.ts

@@ -11,7 +11,7 @@ const createFormatter = (min: number, max: number, opts: MaskOptions): Intl.Numb
   })
 
 export const processNumber = (value: string, masked = true, opts: MaskOptions): string => {
-  const sign = opts.number?.unsigned == null && value.startsWith('-') ? '-' : ''
+  const sign = opts.number?.unsigned !== true && value.startsWith('-') ? '-' : ''
   const fraction = opts.number?.fraction ?? 0
 
   let formatter = createFormatter(0, fraction, opts)

test/number.test.ts

@@ -88,6 +88,14 @@ test('unsigned number', () => {
   expect(mask.masked('--1')).toBe('1')
 })
 
+test('unsigned false number', () => {
+  const mask = new Mask({ number: { unsigned: false } })
+
+  expect(mask.masked('1')).toBe('1')
+  expect(mask.masked('-1')).toBe('-1')
+  expect(mask.masked('--1')).toBe('-1')
+})
+
 test('russian number', () => {
   const mask = new Mask({ number: { locale: 'ru', fraction: 2 } })