(fix): fix broken dotSize function

- this fixes an error that occurred when drawing a single dot that
  would result in the canvas looking empty and the state of the
  component containing a blank image

- this error was introduced in the v0.1.6 release that made dotSize
  a static function instead of defined in the constructor
  - (props to @kgram for catching this in #11)

Author: lopis

README.md

@@ -42,7 +42,7 @@ used in drawing. All props are **optional**.
 - `minWidth` : `number`, default: `0.5`
 - `maxWidth` : `number`, default: `2.5`
 - `dotSize` : `number` or `function`,
-  default: `() => (this.props.minWidth + this.props.maxWidth) / 2`
+  default: `(minWidth, maxWidth) => (minWidth + maxWidth) / 2`
 - `penColor` : `string`, default: `'black'`
 
 There are also two callbacks that will be called when a stroke ends and one

src/index.js

@@ -22,8 +22,8 @@ export default class SignatureCanvas extends Component {
     velocityFilterWeight: 0.7,
     minWidth: 0.5,
     maxWidth: 2.5,
-    dotSize: () => {
-      return (this.props.minWidth + this.props.maxWidth) / 2
+    dotSize: (minWidth, maxWidth) => {
+      return (minWidth + maxWidth) / 2
     },
     penColor: 'black',
     onEnd: () => {},
@@ -208,7 +208,7 @@ export default class SignatureCanvas extends Component {
   _strokeDraw = (point) => {
     let ctx = this._ctx
     let dotSize = typeof(this.props.dotSize) === 'function'
-      ? this.props.dotSize()
+      ? this.props.dotSize(this.props.minWidth, this.props.maxWidth)
       : this.props.dotSize
 
     ctx.beginPath();