avoid nightly rust for cargo fuzz

An older version of proc-macro2 used by many crates doesn't compile
on nightly rust any more.  It doesn't look like we need nightly
rust for cargo-fuzz any more, so try using stable rust instead.

.github/workflows/termwiz.yml

@@ -53,8 +53,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v3
-      - name: "Install Rust"
-        uses: dtolnay/rust-toolchain@nightly
+      - name: "Install Stable Rust"
+        uses: dtolnay/rust-toolchain
       - name: "Cache cargo"
         uses: Swatinem/rust-cache@v2
         with:
@@ -69,5 +69,5 @@ jobs:
         run: |
           source $HOME/.cargo/env
           cd termwiz/fuzz
-          RUST_BACKTRACE=full cargo +nightly fuzz run escape_parse -- -max_total_time=60
+          RUST_BACKTRACE=full cargo fuzz run escape_parse -- -max_total_time=60