fix(SSR): Consolidate dual-regex approach to single regex

fix vuejs#7859

Author: brophdawg11

src/platforms/web/compiler/modules/class.js

@@ -22,7 +22,7 @@ function transformNode (el: ASTElement, options: CompilerOptions) {
     }
   }
   if (staticClass) {
-    el.staticClass = JSON.stringify(staticClass.replace(/\n/g, ' ').replace(/ +/g, ' '))
+    el.staticClass = JSON.stringify(staticClass.replace(/\s+/g, ' '))
   }
   const classBinding = getBindingAttr(el, 'class', false /* getStatic */)
   if (classBinding) {

test/ssr/ssr-string.spec.js

@@ -1228,7 +1228,7 @@ describe('SSR: renderToString', () => {
   })
 
   // #7859
-  it('should trim excess whigtespace in class attributes', done => {
+  it('should trim excess whitespace in class attributes', done => {
     renderVmWithOptions({
       template: `
       <div>