Update comment in build.rs

build.rs

@@ -45,7 +45,7 @@ struct Version {
 
 impl Version {
     // The version detection logic is based on https://github.com/cuviper/autocfg/blob/1.0.1/src/version.rs#L25-L59,
-    // but provides a better error message.
+    // but detects channel and provides a better error message.
     fn from_rustc(rustc: &Path) -> Result<Self, String> {
         let output =
             Command::new(rustc).args(&["--version", "--verbose"]).output().map_err(|e| {