Fix no_std build

Author: vks

src/lib.rs

@@ -704,9 +704,9 @@ pub fn extended_gcd<T: Integer + NumRef>(a: T, b: T) -> GcdResult<T>
 
     while r != T::zero() {
         let quotient = &old_r / &r;
-        old_r = old_r - &quotient * &r; std::mem::swap(&mut old_r, &mut r);
-        old_s = old_s - &quotient * &s; std::mem::swap(&mut old_s, &mut s);
-        old_t = old_t - quotient * &t; std::mem::swap(&mut old_t, &mut t);
+        old_r = old_r - &quotient * &r; mem::swap(&mut old_r, &mut r);
+        old_s = old_s - &quotient * &s; mem::swap(&mut old_s, &mut s);
+        old_t = old_t - quotient * &t; mem::swap(&mut old_t, &mut t);
     }
 
     let _quotients = (t, s); // == (a, b) / gcd