Upgrade to a new rust-toolchain file

Xanewok · Xanewok · commit ee1af6288b48 · 2021-05-26T13:25:42.000+02:00
diff --git a/rust-toolchain b/rust-toolchain
@@ -1 +1,3 @@
-nightly
+[toolchain]
+channel = "nightly-2021-05-19"
+components = ["rust-src", "rustc-dev", "llvm-tools-preview"]
