Fix highlight of functions in CPP lexer (#1928)

This fixes a bug where closing bracket does not pops out of the function
state and causes subsequent functions not to be highlighted correctly.
This change ensures closing bracket in statements mixin is detecting
function state.

lib/rouge/lexers/cpp.rb

@@ -71,7 +71,11 @@ def self.reserved
         rule %r/\bnullptr\b/, Name::Builtin
         rule %r/(?:u8|u|U|L)?R"([a-zA-Z0-9_{}\[\]#<>%:;.?*\+\-\/\^&|~!=,"']{,16})\(.*?\)\1"/m, Str
         rule %r/(::|<=>)/, Operator
-        rule %r/[{}]/, Punctuation
+        rule %r/[{]/, Punctuation
+        rule %r/}/ do
+          token Punctuation
+          pop! if in_state?(:function) # pop :function
+        end
       end
 
       state :classname do