[guide] Fix chaining example to be consistent with string interpolation

Author: wachunei

README.md

@@ -2174,7 +2174,7 @@ Other Style Guides
     // bad
     const leds = stage.selectAll('.led').data(data).enter().append('svg:svg').classed('led', true)
         .attr('width', (radius + margin) * 2).append('svg:g')
-        .attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')')
+        .attr('transform', `translate(${radius + margin},${radius + margin})`)
         .call(tron.led);
 
     // good
@@ -2184,7 +2184,7 @@ Other Style Guides
         .classed('led', true)
         .attr('width', (radius + margin) * 2)
       .append('svg:g')
-        .attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')')
+        .attr('transform', `translate(${radius + margin},${radius + margin})`)
         .call(tron.led);
 
     // good