Update source/containers.tex

Co-authored-by: Johel Ernesto Guerrero Peña <johelegp@gmail.com>

Author: jensmaurer

source/containers.tex

@@ -15233,7 +15233,7 @@
 Since this operation performs an in-place merge, it may allocate memory.
 \end{itemdescr}
 
-\indexlibrarymember{try_emplace}{flatmap}%
+\indexlibrarymember{try_emplace}{flat_map}%
 \begin{itemdecl}
 template<class... Args>
   pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);