Fix avatar scaling on high-DPI displays (#573)

app/assets/javascripts/components/components/avatar.jsx

@@ -25,7 +25,7 @@ const Avatar = React.createClass({
   },
 
   handleLoad () {
-    this.canvas.getContext('2d').drawImage(this.image, 0, 0, this.props.size, this.props.size);
+    this.canvas.getContext('2d').drawImage(this.image, 0, 0, this.props.size * window.devicePixelRatio, this.props.size * window.devicePixelRatio);
   },
 
   setImageRef (c) {
@@ -42,7 +42,7 @@ const Avatar = React.createClass({
     return (
       <div onMouseEnter={this.handleMouseEnter} onMouseLeave={this.handleMouseLeave} style={{ ...this.props.style, width: `${this.props.size}px`, height: `${this.props.size}px`, position: 'relative' }}>
         <img ref={this.setImageRef} onLoad={this.handleLoad} src={this.props.src} width={this.props.size} height={this.props.size} alt='' style={{ position: 'absolute', top: '0', left: '0', visibility: hovering ? 'visible' : 'hidden', borderRadius: '4px' }} />
-        <canvas ref={this.setCanvasRef} width={this.props.size} height={this.props.size} style={{ borderRadius: '4px' }} />
+        <canvas ref={this.setCanvasRef} width={this.props.size * window.devicePixelRatio} height={this.props.size * window.devicePixelRatio} style={{ borderRadius: '4px', width: this.props.size, height: this.props.size }} />
       </div>
     );
   }