[depr.atomics] Fix <atomic> header name. (#3948)

jensmaurer · zygoloid · commit 883bed866014 · 2020-09-22T12:09:45.000-07:00
The typo was introduced in commit bbb4626 while applying P0883R2 Fixing Atomic Initialization.
diff --git a/source/future.tex b/source/future.tex
@@ -2677,7 +2677,7 @@
 \rSec2[depr.atomics.general]{General}
 
 \pnum
-The header \libheaderref{atomics} has the following additions.
+The header \libheaderrefx{atomic}{atomics.syn} has the following additions.
 
 \begin{codeblock}
 namespace std {
