Fix memory leak

If `fread` fails, `file_contents` is leaked.  I’m just freeing the memory allocated :)

parson.c

@@ -161,6 +161,7 @@ static char * read_file(const char * filename) {
     if (fread(file_contents, file_size, 1, fp) < 1) {
         if (ferror(fp)) {
             fclose(fp);
+            parson_free(file_contents);
             return NULL;
         }
     }