Bump minimum Rust version in Mk/Uses/cargo.mk

Given that at least ripgrep will soon require Rust >= 1.28.0 [1]
and given the recently discovered buffer overflow vulnerability in
the standard library of Rust < 1.29.1 [2] bump it to 1.29.1 to avoid
surprises.

[1] BurntSushi/ripgrep#1019
[2] https://groups.google.com/forum/#!topic/rustlang-security-announcements/CmSuTm-SaU0


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@480877 35697150-7ecd-e111-bb59-0022644237b5

Mk/Uses/cargo.mk

@@ -46,7 +46,7 @@ DISTFILES+=	${CARGO_DIST_SUBDIR}/${_crate}.tar.gz:cargo_${_crate:S/-//g:S/.//g}
 
 CARGO_BUILDDEP?=	yes
 .if ${CARGO_BUILDDEP:tl} == "yes"
-BUILD_DEPENDS+=	 rust>=1.19.0_2:lang/rust
+BUILD_DEPENDS+=	 rust>=1.29.1:lang/rust
 .endif
 
 # Location of cargo binary (default to lang/rust's Cargo binary)