[atomics.syn] Fix typo by replacing ')' with '_'

Fixes #359

Author: jwakely

source/atomics.tex

@@ -83,7 +83,7 @@
     memory_order, memory_order) noexcept;
   bool atomic_compare_exchange_weak_explicit(@\textit{atomic-type}@*, T*, T,
     memory_order, memory_order) noexcept;
-  bool atomic_compare)exchange_strong_explicit(volatile @\textit{atomic-type}@*, T*, T,
+  bool atomic_compare_exchange_strong_explicit(volatile @\textit{atomic-type}@*, T*, T,
     memory_order, memory_order) noexcept;
   bool atomic_compare_exchange_strong_explicit(@\textit{atomic-type}@*, T*, T,
     memory_order, memory_order) noexcept;