scribble: another Unicode mapping for Latex output

This mapping is needed by the "redex-unstable" documentation.

Merge to v6.1
(cherry picked from commit a33c64b45f)

pkgs/scribble-pkgs/scribble-lib/scribble/latex-render.rkt

@@ -1002,6 +1002,8 @@
                             [(#\”) "{''}"]
                             [(#\u2013) "{--}"]
                             [(#\u2014) "{---}"]
+                            [(#\〈) "$\\langle$"]
+                            [(#\〉) "$\\rangle$"]
                             [(#\∞) "$\\infty$"]
                             [(#\⇓) "$\\Downarrow$"]
                             [(#\↖) "$\\nwarrow$"]