Fixed #453 - Can't type - as first symbol into an Inputnumber

src/components/inputnumber/InputNumber.vue

@@ -165,6 +165,10 @@ export default {
         },
         formatValue(value) {
             if (value != null) {
+                if (value === '-') { // Minus sign
+                    return value;
+                }
+
                 if (this.format) {
                     let formatter = new Intl.NumberFormat(this.locale, this.getOptions());
                     let formattedValue = formatter.format(value);
@@ -196,6 +200,9 @@ export default {
                                 .replace(this._numeral, this._index);
 
             if (filteredText) {
+                if (filteredText === '-') // Minus sign
+                    return filteredText;
+
                 let parsedValue = +filteredText;
                 return isNaN(parsedValue) ? null : parsedValue;
             }