remove the const attribute

include/nlohmann/detail/input/input_adapters.hpp

@@ -53,17 +53,17 @@ Input adapter for stdio file access. This adapter read only 1 byte and do not us
 class file_input_adapter : public input_adapter_protocol
 {
   public:
-    explicit file_input_adapter(const FILE* file)  noexcept
+    explicit file_input_adapter(FILE* file)  noexcept
         : file(file)
     {}
 
     std::char_traits<char>::int_type get_character() noexcept override
     {
-        return fgetc(const_cast<FILE*>(file));
+        return fgetc(file);
     }
   private:
     /// the file pointer to read from
-    const FILE* file;
+    FILE* file;
 };