fix single-letter hyphenated props (fix #3187)

Author: yyx990803

src/util/lang.js

@@ -189,9 +189,10 @@ function toUpper (_, c) {
  * @return {String}
  */
 
-var hyphenateRE = /([a-z\d])([A-Z])/g
+var hyphenateRE = /([^-])([A-Z])/g
 export function hyphenate (str) {
   return str
+    .replace(hyphenateRE, '$1-$2')
     .replace(hyphenateRE, '$1-$2')
     .toLowerCase()
 }

test/unit/specs/util/lang_spec.js

@@ -51,6 +51,7 @@ describe('Util - Language Enhancement', function () {
     expect(_.hyphenate('fooBar')).toBe('foo-bar')
     expect(_.hyphenate('a1BfC')).toBe('a1-bf-c')
     expect(_.hyphenate('already-With-Hyphen')).toBe('already-with-hyphen')
+    expect(_.hyphenate('ABigApple')).toBe('a-big-apple')
   })
 
   it('classify', function () {