net-im/matterbridge: Switch to USES=go:modules, fix build with go1.13

- Remove custom targets

===>  Building for matterbridge-1.14.4
$GOPATH/go.mod exists but should not
*** Error code 1

PR:		239882
Submitted by:	Dmitri Goutnik <dg@syrec.org>
Approved by:	swills (maintainer timeout, 15 days)

net-im/matterbridge/Makefile

@@ -11,11 +11,10 @@ COMMENT=	Chat network bridge
 LICENSE=	APACHE20
 LICENSE_FILE=	${WRKSRC}/LICENSE
 
-USES=		go
+USES=		go:modules
 
 USE_GITHUB=	yes
 GH_ACCOUNT=	42wim
-GH_SUBDIR=	src/github.com/42wim/matterbridge
 
 USE_RC_SUBR=	matterbridge
 
@@ -30,12 +29,7 @@ PLIST_SUB=	\
 		MATTERBRIDGE_USER=${MATTERBRIDGE_USER} \
 		MATTERBRIDGE_GROUP=${MATTERBRIDGE_GROUP}
 
-do-build:
-	@cd ${WRKSRC}/src/github.com/42wim/matterbridge && \
-		${SETENV} ${MAKE_ENV} GOPATH=${WRKSRC} go build -o bin/${PORTNAME}
-
-do-install:
-	${INSTALL_PROGRAM} ${WRKSRC}/bin/${PORTNAME} ${STAGEDIR}${PREFIX}/bin
+post-install:
 	${INSTALL_DATA} ${WRKSRC}/matterbridge.toml.sample ${STAGEDIR}${PREFIX}/etc/matterbridge.toml.sample
 
 .include <bsd.port.mk>