C++14 single quote (') digit separators aren't rendered correctly in header files

[ewalt1]

https://en.cppreference.com/w/cpp/language/integer_literal

If I do something like:

static constexpr int kThisIsOdd = 0b1111'1111;

Then it will treat the ' as a character capture sequence and render all of the subsequent font as green. The same thing works fine in .cc files.