Merge pull request #1931 from NanXiao/patch-1

A small typo?

src/ch03-01-variables-and-mutability.md

@@ -65,7 +65,7 @@ But mutability can be very useful. Variables are immutable only by default; as
 you did in Chapter 2, you can make them mutable by adding `mut` in front of the
 variable name. In addition to allowing this value to change, `mut` conveys
 intent to future readers of the code by indicating that other parts of the code
-will be changing this variable value.
+will be changing this variable's value.
 
 For example, let’s change *src/main.rs* to the following: