fix warning in civetweb.c

include/civetweb.h

@@ -61,7 +61,7 @@ struct mg_request_info {
                                    NULL */
     const char *remote_user;    /* Authenticated user, or NULL if no auth
                                    used */
-    const char remote_addr[48]; /* Client's IP address as a string. */
+    char remote_addr[48];       /* Client's IP address as a string. */
     long remote_ip;             /* Client's IP address. Deprecated: use remote_addr instead */
 
     long long content_length;   /* Length (in bytes) of the request body,