Tweak comment

core/blockly.js

@@ -62,7 +62,8 @@ goog.requireType('Blockly.Workspace');
 /**
  * Blockly core version.
  * This constant is overridden by the build script (npm run build) to the value
- * of the version in package.json. This is done during the gen_core build step.
+ * of the version in package.json. This is done by the Closure Compiler in the
+ * buildCompressed gulp task.
  * For local builds, you can pass --define='Blockly.VERSION=X.Y.Z' to the
  * compiler to override this constant.
  * @define {string}