Override rustup toolchain with stable

It is better to specify explicitly which toolchain to use when building with cargo because
- user may override default rustup toolchain with an incompatible one
- user may isolate builds / uses jails. Some AUR helpers are automating this (ie: [rua](https://github.com/vn971/rua#safety)). In such case following error may be produced and build fails: `error: no override and no default toolchain set`

1 files changed, 1 insertions, 0 deletions

diff --git a/PKGBUILD b/PKGBUILD
index 1f452b9b6949..dc79f4b3e6d9 100644
--- a/PKGBUILD
+++ b/PKGBUILD
@@ -27,6 +27,7 @@ build() {
   cd "${srcdir}/${pkgname}-${pkgver}"
   export CARGO_HOME="${srcdir}/${pkgname}/CARGO"
   export CFLAGS="-fcommon -fPIE"
+  export RUSTUP_TOOLCHAIN=stable
   cargo build --release
 }