fix malloc() return value cast to pointer of InputBuffer

Author: stardustman

_parts/part1.md

@@ -90,7 +90,7 @@ typedef struct {
 } InputBuffer;
 
 InputBuffer* new_input_buffer() {
-  InputBuffer* input_buffer = malloc(sizeof(InputBuffer));
+  InputBuffer* input_buffer = (InputBuffer*)malloc(sizeof(InputBuffer));
   input_buffer->buffer = NULL;
   input_buffer->buffer_length = 0;
   input_buffer->input_length = 0;