Call svgResize in the resize handler.

Resolves #2000

demos/resizable/overlay.html

@@ -86,6 +86,7 @@
       blocklyDiv.style.top = y + 'px';
       blocklyDiv.style.width = blocklyArea.offsetWidth + 'px';
       blocklyDiv.style.height = blocklyArea.offsetHeight + 'px';
+      Blockly.svgResize(demoWorkspace);
     };
     window.addEventListener('resize', onresize, false);
     onresize();