[stacktrace.format] Use full typename "basic_stacktrace<Allocator>".

Author: tkoeppe

Diff for: source/diagnostics.tex

@@ -2438,7 +2438,7 @@
 \fmtgrammarterm{format-spec} is empty.
 
 \pnum
-A \tcode{basic_stacktrace} object \tcode{s} is formatted as if by
+A \tcode{basic_stacktrace<Allocator>} object \tcode{s} is formatted as if by
 copying \tcode{to_string(s)} through the output iterator of the context.
 \end{itemdescr}