src: make operator napi_callback_info explicit

PR-URL: #1275
Reviewed-By: JckXia <[email protected]>
Reviewed-By: Michael Dawson <[email protected]

Author: KevinEady

napi.h

@@ -1794,7 +1794,7 @@ class CallbackInfo {
   Value This() const;
   void* Data() const;
   void SetData(void* data);
-  operator napi_callback_info() const;
+  explicit operator napi_callback_info() const;
 
  private:
   const size_t _staticArgCount = 6;