Docs: ensure presence of constructor description

lib/constructor.js

@@ -38,8 +38,6 @@ try {
 const debuglog = util.debuglog('sharp');
 
 /**
- * @constructs sharp
- *
  * Constructor factory to create an instance of `sharp`, to which further methods are chained.
  *
  * JPEG, PNG, WebP or TIFF format image data can be streamed out from this object.
@@ -49,6 +47,8 @@ const debuglog = util.debuglog('sharp');
  *
  * Implements the [stream.Duplex](http://nodejs.org/api/stream.html#stream_class_stream_duplex) class.
  *
+ * @constructs Sharp
+ *
  * @emits Sharp#info
  * @emits Sharp#warning
  *