made DataEvent::data unique_ptr non-const

src/uvw/stream.hpp

@@ -62,11 +62,11 @@ struct WriteEvent: Event<WriteEvent> { };
  * It will be emitted by StreamHandle according with its functionalities.
  */
 struct DataEvent: Event<DataEvent> {
-    explicit DataEvent(std::unique_ptr<const char[]> data, ssize_t length) noexcept
+    explicit DataEvent(std::unique_ptr<char[]> data, ssize_t length) noexcept
         : data{std::move(data)}, length(length)
     { }
 
-    std::unique_ptr<const char[]> data; /*!< A bunch of data read on the stream. */
+    std::unique_ptr<char[]> data; /*!< A bunch of data read on the stream. */
     std::size_t length; /*!< The amount of data read on the stream. */
 };