Update custom.md

Author: xtexChooser

src/doc/rustc/src/targets/custom.md

@@ -5,13 +5,13 @@ If you'd like to build for a target that is not yet supported by `rustc`, you ca
 are JSON. To see the JSON for the host target, you can run:
 
 ```bash
-$ rustc +nightly -Z unstable-options --print target-spec-json
+rustc +nightly -Z unstable-options --print target-spec-json
 ```
 
 To see it for a different target, add the `--target` flag:
 
 ```bash
-$ rustc +nightly -Z unstable-options --target=wasm32-unknown-unknown --print target-spec-json
+rustc +nightly -Z unstable-options --target=wasm32-unknown-unknown --print target-spec-json
 ```
 
 To use a custom target, see the (unstable) [`build-std` feature](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#build-std) of `cargo`.