updata src/conversion/from_into.md (#198)

* update src/cargo/conventions.md

* updata src/conversion/from_into.md

english/src/conversion/from_into.md

@@ -51,22 +51,22 @@ convert into as the compiler is unable to determine this most of the time.
 However this is a small trade-off considering we get the functionality for free.
 
 ```rust,editable
-use std::convert::From;
+use std::convert::Into;
 
 #[derive(Debug)]
 struct Number {
     value: i32,
 }
 
-impl From<i32> for Number {
-    fn from(item: i32) -> Self {
-        Number { value: item }
+impl Into<Number> for i32 {
+    fn into(self) -> Number {
+        Number { value: self }
     }
 }
 
 fn main() {
     let int = 5;
-    // Try removing the type declaration
+    // Try removing the type annotation
     let num: Number = int.into();
     println!("My number is {:?}", num);
 }

src/conversion/from_into.md

@@ -42,22 +42,22 @@ fn main() {
 使用 `Into` trait 通常要求指明要转换到的类型，因为编译器大多数时候不能推断它。不过考虑到我们免费获得了 `Into`，这点代价不值一提。
 
 ```rust,editable
-use std::convert::From;
+use std::convert::Into;
 
 #[derive(Debug)]
 struct Number {
     value: i32,
 }
 
-impl From<i32> for Number {
-    fn from(item: i32) -> Self {
-        Number { value: item }
+impl Into<Number> for i32 {
+    fn into(self) -> Number {
+        Number { value: self }
     }
 }
 
 fn main() {
     let int = 5;
-    // 试试删除类型说明
+    // 试试删除类型注释
     let num: Number = int.into();
     println!("My number is {:?}", num);
 }