[except.spec] Add missing '~' in comment in example.

Thanks to Sergey P. Derevyago for reporting this!

Author: zygoloid

source/exceptions.tex

@@ -920,7 +920,7 @@
     // \tcode{D::D()} potentially-throwing, as the \tcode{new} operator may throw \tcode{bad_alloc} or \tcode{bad_array_new_length}
     // \tcode{D::D(const D\&)} non-throwing
     // \tcode{D::D(D\&\&)} potentially-throwing, as the default argument for \tcode{B}'s constructor may throw
-    // \tcode{D::~D()} potentially-throwing
+    // \tcode{D::\~D()} potentially-throwing
 };
 \end{codeblock}
 Furthermore, if