[fs.op.copy] Fix indentation

Author: Andreas-Krug

source/iostreams.tex

@@ -17254,7 +17254,7 @@
 \begin{itemdecl}
 void filesystem::copy(const path& from, const path& to, copy_options options);
 void filesystem::copy(const path& from, const path& to, copy_options options,
-          error_code& ec);
+                      error_code& ec);
 \end{itemdecl}
 
 \begin{itemdescr}