Fix using namespace

We inherited a "using namespace" crow.  Lets fix it.

Tested:
Code compiles.  No functional changes.

Signed-off-by: Ed Tanous <ed@tanous.net>
Change-Id: Id47446150dfb312c5cd84a4b4284fb824eba8021
diff --git a/http/app.h b/http/app.h
index 2eca4d2..ff8642d 100644
--- a/http/app.h
+++ b/http/app.h
@@ -211,7 +211,7 @@
 #endif
 
   private:
-    std::shared_ptr<asio::io_context> io;
+    std::shared_ptr<boost::asio::io_context> io;
 #ifdef BMCWEB_ENABLE_SSL
     uint16_t portUint = 443;
 #else