[improvement] rename suffixPx to addUnit

src/utils/format/unit.ts

@@ -1,7 +1,7 @@
 import { isDef } from '..';
 import { isNumber } from '../validate/number';
 
-export function suffixPx(value?: string | number): string | undefined {
+export function addUnit(value?: string | number): string | undefined {
   if (!isDef(value)) {
     return undefined;
   }

src/utils/index.ts

@@ -1,7 +1,7 @@
 import Vue from 'vue';
 
 export { createNamespace } from './create';
-export { suffixPx } from './format/unit';
+export { addUnit } from './format/unit';
 
 export const isServer: boolean = Vue.prototype.$isServer;