make don't know how to make-crates

Hello,

I'm trying to make my first port on FreeBSD with sendxmpp-rs (
https://github.com/moparisthebest/sendxmpp-rs ).
I wrote the following _Makefile_:

```
PORTNAME=			sendxmpp-rs
PORTVERSION=		2.0.0
DISTVERSIONPREFIX=	v
CATEGORIES=			net-im

MAINTAINER=			rollniak@courrier.dev
COMMENT=			Send XMPP messages from the command
line.

USE=				cargo
USE_GITHUB=			yes
GH_ACCOUNT=			moparisthebest
CONFLICTS=			sendxmpp
```

And executed `make makesum`:

```
$ make makesum
===>   sendxmpp-rs-2.0.0 depends on file: /usr/local/sbin/pkg - found
===> Fetching all distfiles required by sendxmpp-rs-2.0.0 for building
```

But when I ran 'make cargo-crates`, I got the following message instead
of a CARGO_CRATES output I expected:

```
make: don't know how to make cargo-crates. Stop

make: stopped in /usr/local/poudriere/ports/devel/net-im/sendxmpp-rs
```

cargo is installed on my machine and based on the content of
_Cargo.toml_ I think I should have another output

_Cargo.toml_:

```
[package]
name = "sendxmpp"
version = "2.0.0"
authors = ["moparisthebest <admin@moparisthebest.com>"]

description = "Send XMPP messages from the command line."
repository  =
"https://code.moparisthebest.com/moparisthebest/sendxmpp-rs"
keywords    = ["xmpp"]

license = "AGPL-3.0-or-later"
readme = "README.md"

edition = "2018"

include = [
    "**/*.rs",
    "Cargo.toml",
    "*.md",
    "sendxmpp.toml",
]

[dependencies]
toml = "0.5"
serde_derive = "1.0"
serde = { version = "1.0", features = ["derive"] }
gumdrop = "0.8.0"
gumdrop_derive = "0.8.0"
dirs = "3.0.1"
tokio-xmpp = "3.0.0"
tokio = { version = "1", features = ["net", "rt",
"rt-multi-thread", "macros", "io-util", "io-std"] }
tokio-tls = { package = "tokio-native-tls", version =
"0.3" }
xmpp-parsers = "0.18"
die = "0.2.0"
anyhow = "1.0"
```

Can someone help me to find out what the output of `make cargo-crates`
mean or give me some hint about how to fix this issue ? :)

Have a nice day,
rollniak