Update advanced.md

Author: GuillaumeGomez

src/doc/trpl/advanced.md

@@ -1,6 +1,6 @@
 % Advanced
 
-In a similar fashion to "Intermediate," this setion is full of individual,
+In a similar fashion to "Intermediate," this section is full of individual,
 deep-dive chapters, which stand alone and can be read in any order. These
 chapters focus on the most complex features, as well as some things that
 are only available in upcoming versions of Rust.