Tidy error: add a new line

The error was:

```
[00:05:25] tidy error: /checkout/src/libcore/num/mod.rs:3848: trailing whitespace
[00:05:25] tidy error: /checkout/src/libcore/num/mod.rs:3851: line longer than 100 chars
[00:05:25] tidy error: /checkout/src/libcore/num/mod.rs:3851: trailing whitespace
[00:05:26] some tidy checks failed
```
The line was truncated to 92 characters.

Author: Songbird0

src/libcore/num/mod.rs

@@ -3848,7 +3848,8 @@ fn from_str_radix<T: FromStrRadixHelper>(src: &str, radix: u32) -> Result<T, Par
 /// 
 /// # Potential causes
 ///
-/// Among other causes, `ParseIntError` can be thrown because of leading or trailing whitespaces in the string e.g. when it is getted from the standard input. 
+/// Among other causes, `ParseIntError` can be thrown because of leading or trailing whitespaces 
+/// in the string e.g. when it is getted from the standard input. 
 /// Using the [`str.trim()`] method ensures that no whitespace remains before parsing.
 ///
 /// [`str.trim()`]: ../../std/primitive.str.html#method.trim