doc: fix an incorrect code comment

Author: yvt

src/constance/src/lib.rs

@@ -19,7 +19,7 @@
 #![doc(include = "./common.md")]
 #![cfg_attr(not(test), no_std)] // Link `std` only when building a test (`cfg(test)`)
 
-// When using `#![no_std]`, `core` has to be imported manually to be used
+// When not using `#![no_std]`, `core` has to be manually imported to be used
 #[cfg(test)]
 extern crate core;