[fix] 'flex' shorthand sets 'flexBasis' to '0%'

Ref #426

src/apis/AppRegistry/__tests__/__snapshots__/renderApplication-test.js.snap

@@ -52,6 +52,7 @@ input::-webkit-inner-spin-button,input::-webkit-outer-spin-button,input::-webkit
 .rn-flexShrink-1qe8dj5{-webkit-flex-shrink:0;flex-shrink:0}
 .rn-flexShrink-1wbh5a2{-webkit-flex-shrink:1;flex-shrink:1}
 .rn-flexBasis-1mlwlqe{-webkit-flex-basis:auto;flex-basis:auto}
+.rn-flexBasis-1ro0kt6{-webkit-flex-basis:0%;flex-basis:0%}
 .rn-flexDirection-eqz5dr{-webkit-box-direction:normal;-webkit-box-orient:vertical;-webkit-flex-direction:column;flex-direction:column}
 .rn-marginTop-1mnahxq{margin-top:0px}
 .rn-marginRight-61z16t{margin-right:0px}

src/apis/StyleSheet/__tests__/createReactDOMStyle-test.js

@@ -32,14 +32,14 @@ describe('apis/StyleSheet/createReactDOMStyle', () => {
       display: 'flex',
       flexGrow: 1,
       flexShrink: 1,
-      flexBasis: 'auto'
+      flexBasis: '0%'
     });
 
     expect(createReactDOMStyle({ display: 'flex', flex: 10 })).toEqual({
       display: 'flex',
       flexGrow: 10,
       flexShrink: 1,
-      flexBasis: 'auto'
+      flexBasis: '0%'
     });
 
     expect(createReactDOMStyle({ display: 'flex', flexShrink: 1 })).toEqual({
@@ -51,7 +51,7 @@ describe('apis/StyleSheet/createReactDOMStyle', () => {
       display: 'flex',
       flexGrow: 1,
       flexShrink: 2,
-      flexBasis: 'auto'
+      flexBasis: '0%'
     });
   });
 

src/apis/StyleSheet/createReactDOMStyle.js

@@ -155,7 +155,7 @@ const createReducer = (style, styleProps) => {
       case 'flex': {
         resolvedStyle.flexGrow = value;
         resolvedStyle.flexShrink = 1;
-        resolvedStyle.flexBasis = 'auto';
+        resolvedStyle.flexBasis = '0%';
         break;
       }
       case 'shadowColor':