Bump Rust nightly version to 2020-08-11

This nightly build includes both rust-lang/rust#72121 and a working
`rustfmt`.

Author: Aaron1011

ci/rust-version.sh

@@ -24,7 +24,7 @@ fi
 if [[ -n $RUST_NIGHTLY_VERSION ]]; then
   nightly_version="$RUST_NIGHTLY_VERSION"
 else
-  nightly_version=2020-07-27
+  nightly_version=2020-08-11
 fi