fix: support decimal step

package.json

@@ -1,6 +1,6 @@
 {
   "name": "rc-slider",
-  "version": "3.1.1",
+  "version": "3.1.2",
   "description": "slider ui component for react",
   "keywords": [
     "react",

src/Slider.jsx

@@ -203,6 +203,16 @@ class Slider extends React.Component {
     return rect.left;
   }
 
+  getPrecision() {
+    const props = this.props;
+    const stepString = props.step.toString();
+    let precision = 0;
+    if (stepString.indexOf('.') >= 0) {
+      precision = stepString.length - stepString.indexOf('.') - 1;
+    }
+    return precision;
+  }
+
   trimAlignValue(v) {
     const state = this.state || {};
     const {handle, lowerBound, upperBound} = state;
@@ -231,7 +241,7 @@ class Slider extends React.Component {
     const diffs = points.map((point) => Math.abs(val - point));
     const closestPoint = points[diffs.indexOf(Math.min.apply(Math, diffs))];
 
-    return closestPoint;
+    return step !== null ? parseFloat(closestPoint.toFixed(this.getPrecision())) : closestPoint;
   }
 
   calcOffset(value) {