fix IsHigh trait comment (#1726)

The comment was saying that function informs if the scalar is **"greater
or equal to"** whereas the implementation informs if the scalar is
**"strictly greater than"**

elliptic-curve/src/scalar.rs

@@ -49,6 +49,6 @@ pub trait FromUintUnchecked {
 /// - For scalars 0 through n / 2: `Choice::from(0)`
 /// - For scalars (n / 2) + 1 through n - 1: `Choice::from(1)`
 pub trait IsHigh {
-    /// Is this scalar greater than or equal to n / 2?
+    /// Is this scalar greater than n / 2?
     fn is_high(&self) -> Choice;
 }