refactor text render

Support G inherit props.
Refactor text render. Text glyphs will perfectly draw along the path

lib/extract/extractFill.js

@@ -1,5 +1,6 @@
 import extractBrush from './extractBrush';
 import extractOpacity from './extractOpacity';
+import _ from 'lodash';
 
 const fillRules = {
     evenodd: 0,
@@ -8,7 +9,8 @@ const fillRules = {
 
 export default function(props) {
     return {
-        fill: extractBrush(props.fill),
+        // default fill is black
+        fill: extractBrush(_.isNil(props.fill) ? '#000' : props.fill),
         fillOpacity: extractOpacity(props.fillOpacity),
         fillRule: fillRules[props.fillRule] === 0 ? 0 : 1
     };