fix apt-get command

Author: softprops

.appveyor.yml

@@ -116,7 +116,7 @@ for:
       - sh: "curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --profile minimal"
       - sh: "PATH=${HOME}/.cargo/bin:$PATH"
       - sh: "rustup target add x86_64-unknown-linux-musl --toolchain stable"
-      - sh: "sudo apt-get install musl-tools"
+      - sh: "sudo apt-get install -y musl-tools"
       - sh: "rustc -V"
       - sh: "cargo -V"