Conditional compilation - Fix typos

Author: Havvy

src/conditional-compilation.md

@@ -267,7 +267,7 @@ mod os;
 > **Note**: The `cfg_attr` can expand to another `cfg_attr`. For example,
 > `#[cfg_attr(linux, cfg_attr(feature = "multithreaded", some_other_attribute))`
 > is valid. This example would be equivalent to
-> `#[cfg_attr(and(linux, feaure ="multithreaded"), some_other_attribute)]`.
+> `#[cfg_attr(all(linux, feature ="multithreaded"), some_other_attribute)]`.
 
 The `cfg_attr` attribute is allowed anywhere attributes are allowed except on
 generic parameters.