net-im/mtxclient: Bump PORTREVISION to fix net-im/nheko build

After the devel/nlohmann-json update in 551e034, net-im/nheko fails
to build due to linking errors unless net-im/mtxclient is rebuilt.

ld: error: undefined symbol:
mtx::events::state::to_json(nlohmann::json_abi_v3_11_3::basic_json<std::__1::map,
std::__1::vector, std::__1::basic_string<char,
std::__1::char_traits<char>, std::__1::allocator<char>>, bool, long,
unsigned long, double, std::__1::allocator,
nlohmann::json_abi_v3_11_3::adl_serializer, std::__1::vector<unsigned
char, std::__1::allocator<unsigned char>>, void>&,
mtx::events::state::Aliases const&) >>> referenced by EventStore.cpp

Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D42886

net-im/mtxclient/Makefile

@@ -1,7 +1,7 @@
 PORTNAME=		mtxclient
 DISTVERSIONPREFIX=	v
 DISTVERSION=		0.9.2
-PORTREVISION=	3
+PORTREVISION=	4
 CATEGORIES=		net-im
 
 MAINTAINER=	adridg@FreeBSD.org