Use mean instead of average in docs

src/lib.rs

@@ -55,7 +55,7 @@
 //!
 //! let mut a: MeanWithError = (1..6).map(Into::into).collect();
 //! a.add(42.);
-//! println!("The average is {} ± {}.", a.mean(), a.error());
+//! println!("The mean is {} ± {}.", a.mean(), a.error());
 //! ```
 
 #![no_std]

src/moments/variance.rs

@@ -10,7 +10,7 @@
 /// use average::Variance;
 ///
 /// let a: Variance = (1..6).map(Into::into).collect();
-/// println!("The average is {} ± {}.", a.mean(), a.error());
+/// println!("The mean is {} ± {}.", a.mean(), a.error());
 /// ```
 #[derive(Debug, Clone)]
 pub struct Variance {