Fix binary literal digit separator in C++ lexer (rouge-ruby#1620)

The C++ lexer uses `_` as a digit separator for binary literals. This
is syntactically incorrect. The digit separator in C++ is `'`. This
commit fixes that error.

Co-authored-by: Stuart <stuart.wheaton@jhuapl.edu>
Co-authored-by: Michael Camilleri <mike@inqk.net>

lib/rouge/lexers/cpp.rb

@@ -63,7 +63,7 @@ def self.reserved
         rule %r((#{dq}[.]#{dq}?|[.]#{dq})(e[+-]?#{dq}[lu]*)?)i, Num::Float
         rule %r(#{dq}e[+-]?#{dq}[lu]*)i, Num::Float
         rule %r/0x\h('?\h)*[lu]*/i, Num::Hex
-        rule %r/0b[01]+(?:_[01]+)*/, Num::Bin
+        rule %r/0b[01]+('[01]+)*/, Num::Bin
         rule %r/0[0-7]('?[0-7])*[lu]*/i, Num::Oct
         rule %r/#{dq}[lu]*/i, Num::Integer
         rule %r/\bnullptr\b/, Name::Builtin

spec/visual/samples/cpp

@@ -1,8 +1,7 @@
-int quote_delims = 100'000'000
-int float_delims = 100.00'00
-int hex_delims = 0xFF'Fa12
-
-int binary = 0b1000;
+int quote_delims = 100'000'000;
+int float_delims = 100.00'00;
+int hex_delims = 0xFF'Fa12;
+int bin_delims = 0b10'1000;
 
 // string literal with encoding-prefix
 char str1[] = u8"UTF-8 string";