Relax requirements for vector_body:

fix: #1567

std::byte is not an arithmetic type, which caused compilation to fail
when it was used in vector_body.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

include/boost/beast/http/vector_body.hpp

@@ -39,8 +39,7 @@ template<class T, class Allocator = std::allocator<T>>
 struct vector_body
 {
 private:
-    static_assert(sizeof(T) == 1 &&
-        std::is_integral<T>::value,
+    static_assert(sizeof(T) == 1,
         "T requirements not met");
 
 public: